Preheat your oven to 375°F (190°C). Grease a 12-cup muffin tin with cooking spray or butter.
In a large mixing bowl, whisk the eggs, milk, salt, pepper, garlic powder, and Italian herbs until well combined.
Add the chopped bell peppers, spinach, tomatoes, red onion, and mushrooms to the egg mixture. Mix until the vegetables are evenly distributed.
Spoon the mixture into the prepared muffin tin, filling each cup about 3/4 full.
Sprinkle the tops with shredded cheese.
Bake in the oven for 20-25 minutes or until the eggs are set and the tops are lightly golden.
Let the bakes cool for a few minutes before removing them from the tin. If desired, garnish with fresh parsley or chives.
Serve warm and enjoy!