Prep muffin tin: Spray twelve-cup muffin tin with cooking spray or line with silicone baking cups. I sprayed the silicone baking cups with spray, just to be on the safe side.
Whisk eggs: Place eggs and egg whites into a large bowl and whisk to combine. Season with salt and pepper.
Sauté vegetables: 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 mix-ins: Add sautéed veggies into the bowl with the whisked eggs. Add in feta and parsley and mix well.
Divide mixture: Pour egg mixture into muffin cups evenly. I used a 1/3 cup measuring cup to pour each one.
Bake: 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.
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.