Spray twelve-cup muffin tin with cooking spray or line with paper or silicone liners. I sprayed the silicone baking cups with spray, just to be on the safe side.
Place eggs and egg whites into a large bowl and whisk to combine. Season with salt and pepper.
Meanwhile, heat a skillet over medium heat with 1 teaspoon oil. Add in chopped veggies (bell pepper, onion, broccoli and mushrooms) and cook for about 5-6 minutes, until they’re a little soft and the onions are fragrant.
Add sautéed veggies into the bowl with the whisked eggs. Add in feta and parsley and mix well.
Pour egg mixture into muffin cups evenly. I used a 1/3 cup measuring cup to pour each one.
Bake for 17-20 minutes, or until the egg cups are no longer jiggly and an inserted toothpick comes out clean. Allow cups to cool and enjoy immediately.
Notes
Storage: If prepping ahead of time, store cooled cups in a sealed container in the fridge. When ready to eat, you can enjoy the cups cold or pop them in the microwave for 30-60 seconds to reheat.