Preheat oven to 350 degrees F and generously grease a standard non stick 12-slot muffin tin with cooking spray. Set aside.
Heat a large non stick skillet over medium heat.
Once hot, add in oil, red pepper, green pepper, and onion, then cook for 5-7 minutes, or until peppers are tender, stirring regularly.
Add in spinach and mushrooms and cook for an additional 2 minutes.
In the last 30 seconds, add in minced garlic.
Season with salt and remove from heat.
Crack eggs/egg whites into a large 4 cup measuring cup, whisk together until smooth, then stir in the cooked vegetables.
Pour the egg/veggie mixture evenly into the prepared muffin pan, then bake for 15-30 minutes, or until the tops are firm to the touch and eggs are cooked.
*If you'd like to use liquid eggs or just egg whites, you'll need 1 1/2 cups total to replace the 4 large eggs and 4 large egg whites in the original recipe.