Mix ground beef, egg, bread crumbs, finely diced 1/2 cup onion, 2 tsp garlic, parsley, salt & pepper, and parmigiano. Mix until combined.
Form into balls 1 inch in diameter, and brown in 2 Tbsp olive oil.
Move meatballs over to one side of the pan, and add the remaining garlic and red pepper flakes. Cook for a minute, and add the crushed tomatoes. Simmer over low heat.
Spread the spinach over the bottom of a pan and top with the meatballs and crushed tomato mixture. Cover with Italian cheese, and bake at 350 for 30 minutes. Top with fresh basil.