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Grilled Flat Iron Steak

Our easy recipe for a Grilled Flat Iron Steak is simple to make and features a surprisingly delicious shiitake mushroom topper! This dish combines the rich, tender textures of perfectly grilled flat iron steak with the earthy tones of sautéed shiitake mushrooms, finished with a hint of raspberry red wine vinegar for an unexpected pop of flavor. Ideal for a hearty dinner, this recipe takes the classic steak-and-mushrooms duo up a notch through simple seasonings and cooking techniques.

Grilled Flat Iron Steak

There is very little in the food world that can beat a good steak, cooked well.

(Not well-done, mind you, because you know my stance on that. Just go eat a hamburger and stop wasting the good stuff. It isn’t “blood” you’re seeing in a medium rare or even a rare steak. Stop being a baby.)

A nice piece of meat doesn’t require a bunch of crazy seasonings and herbs. Just some salt and pepper is all it needs to really let the meat shine.

At least, that’s what I thought until Jeremiah whipped up this shiitake mushroom topper. I’d eat that with a spoon over any piece of meat, anytime. Now, as much as I love that simple salt and pepper – I’m going to be thinking about these mushrooms for YEARS, or at least until I get to have them again.

Thankfully they are simple to make, so the next time the fresh shiitake look good you can bet that I’ll be loading up on those and some nice steaks for a repeat of this dish.

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Why you’ll love this dish…

  • Rich and Robust Flavors: The steak itself is a flavor powerhouse, and when combined with the umami of shiitake mushrooms, it’s unbeatable.
  • Perfect Grilling Technique: Grilling steak is probably the easiest thing you can cook with the biggest payoff.
  • Simple, High-Quality Ingredients: Few ingredients are used, but each is chosen for its high impact on the overall taste.
  • Versatile Serving Options: Serve as is for a low-carb option, or add sides like mashed potatoes or green beans for a fuller meal.
  • Quick and Easy: Despite its gourmet appeal, this dish comes together quickly, making it perfect for a last-minute dinner party.

Get 75+ of my favorite Traeger Recipes here!

Grilled Flat Iron Steak

Flat Iron Steak shopping list

Wondering if you have to hit the store? Here’s the list of items you’ll need to make this recipe. For specific amounts, please refer to the printable recipe card at the bottom of the post.

  • Flat Iron steaks
  • Salt
  • Pepper
  • Fresh Shiitake Mushrooms
  • Butter
  • Raspberry Red Wine Vinegar

Serve with a Smoked Baked Potato!

Grilled Flat Iron Steak

How to make a Flat Iron on the Grill

Wondering what you’re getting yourself into when you make this dish? Here’s a quick overview of the process! Make sure you follow the instructions at the recipe card at the bottom of the post while you’re cooking.

  • Preheat Grill:
    Start by heating your grill to a medium-high temperature range of 400-425°F.
  • Season Steaks:
    Rub both sides of each steak with salt and pepper to ensure they’re well-seasoned before grilling.
  • Grill Steaks:
    Place the steaks on the grill grates and cook until they reach your desired level of doneness, flipping once midway through cooking.
  • Prepare Mushroom Topper:
    While the steaks grill, sauté chopped shiitake mushrooms in butter, season with salt, and finish with a splash of raspberry red wine vinegar.
  • Rest and Serve:
    Let the grilled steaks rest for a few minutes, then top with the sautéed mushrooms before serving.

Serve with some One-Pot Parmesan Noodles with Asparagus!

Grilled Flat Iron Steak

Grilled Flat Iron FAQ

How long should I grill the steaks?

For medium-rare, aim for an internal temperature of 130°F, usually 6-7 minutes per side.

Can I prepare the Mushroom Topper in advance?

Yes, you can sauté the mushrooms ahead of time and reheat them when ready to serve.

Are there substitutions for shiitake mushrooms?

Button or cremini mushrooms can be used as substitutes, though they will slightly alter the flavor profile.

Try with a Homemade Caesar Salad!

Grilled Flat Iron Steak
Grilled Flat Iron Steak

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Grilled Flat Iron Steak

Grilled Flat Iron Steak with Shiitake Mushrooms

These amazing steaks are perfect to serve to your friends and family! Perfectly cooked, and this mushroom topper will be making many appearances on your table.
5 from 1 vote
Print Pin Rate
Course: Traeger Recipes
Cuisine: American
Keyword: mushroom, steak
Prep Time: 15 minutes
Cook Time: 45 minutes
Total Time: 1 hour
Servings: 4 people
Author: Nicole Johnson


  • 4 8 ounce flat iron steaks
  • 2 tablespoons salt
  • 1 teaspoon freshly ground black pepper

Mushroom Topper

  • 1/2 pound fresh shiitake mushrooms
  • 1/4 teaspoon salt
  • 2 tablespoons butter
  • 1 teaspoon raspberry red wine vinegar


  • Preheat your grill to 400-425°F.
  • Season the steaks evenly with the salt and pepper.
  • Once the grill is preheated, place the steaks in the grill on the grates.
  • While the steaks are cooking, prepare the mushrooms.
  • Chop the mushrooms into small 1/4” pieces. Place them in a medium-size saucepan over medium heat.
  • Add the butter and let it melt while stirring the mushrooms into the melted butter.
  • Add the salt and stir again.
  • Sauté until the mushrooms are fully cooked and slightly browned on the edges.
  • Add the vinegar and stir in.
  • Turn off the heat and let sit for 1-2 minutes. Keep warm until the steaks are done.
  • After 6-7 minutes, flip the steaks and continue cooking until the internal temperature reaches your desired finishing temperature. For medium-rare, we pull the steaks at 130°F.
  • Pull from the grill and let rest for 5-10 minutes before serving.
  • Top with the mushrooms and serve while hot.


Calories: 470kcalCarbohydrates: 4gProtein: 44gFat: 30gSaturated Fat: 13gPolyunsaturated Fat: 1gMonounsaturated Fat: 11gTrans Fat: 1gCholesterol: 165mgSodium: 3852mgPotassium: 883mgFiber: 2gSugar: 1gVitamin A: 178IUVitamin C: 0.01mgCalcium: 21mgIron: 6mg
Nicole Johnson

Nicole Johnson, a self-taught expert in grilling and outdoor cooking, launched Or Whatever You Do in 2010. Her blog, renowned for its comprehensive and creative outdoor cooking recipes, has garnered a vast audience of millions. Nicole's hands-on experience and passion for grilling shine through her work. Her husband, Jeremiah Johnson, also plays a pivotal role in recipe development, adding his culinary flair to the mix. Together, they form a dynamic duo, offering a rich and varied outdoor cooking experience to their followers.

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