Gather all ingredients.

Whisk egg whites and egg together in a small bowl. Mix in Parmesan, Cheddar, salt, red pepper flakes, garlic powder, nutmeg, and pepper.

Heat oil in a large skillet over medium heat. Sauté mushrooms, green onions, and bell pepper until tender, about 5 minutes.

Add spinach and cook until just wilted, 1 to 2 minutes. Stir in tomato, then pour in egg mixture. As egg mixture starts to set, lift the edges and let the uncooked portion flow underneath.

Cook until egg mixture sets, 10 to 15 minutes. Cut into wedges and serve immediately.