Spray a 9” deep pie pan with non-stick baking spray; set pan aside. (Note: This casserole can also be baked in a traditional rectangular casserole dish. The baking time will vary based on the size of the pan, though.)

Preheat oven to 375°F.

Using a large mixing bowl, add the eggs, milk, salt, pepper and crushed red pepper flakes; beat until well combined. Set bowl aside.

Using a large skillet, add butter and olive oil and place over medium heat. Once butter has melted, add the diced onions and bell peppers. Sauté, stirring occasionally, for 3-4 minutes. Transfer onions and peppers into bowl with the egg mixture.

Add sliced mushrooms to the skillet and place over medium heat.

Sauté for 3-4 minutes without stirring. Flip mushrooms over and continue sautéing for 3-4 more minutes without stirring. Transfer mushrooms into bowl with the egg mixture.

Add ham, spinach and shredded cheese to the egg mixture; stir until well combined.

Pour mixture into the prepared pan. Bake uncovered for 55-60 minutes, or until eggs are set. (Note: Tent the casserole after 40 minutes to prevent the top from browning too much.)

Let casserole cool for 5-10 minutes before slicing and serving.