Preheat the oven to 350F, and liberally grease a regular sized muffin tin using cooking spray or cooking oil. In a medium sized bowl, add the eggs, milk, garlic powder, salt and pepper.
Whisk the above ingredients until all yolks are broken and ingredients are just incorporated. Do not overmix as this will add air pockets to your mini frittatas.
In your prepared muffin tin, add an equal portion of the chopped bell pepper to each muffin well.
Equally distribute the fresh spinach leaves into the muffin cups over the green bell pepper.
Top each muffin cup with feta cheese.
Disperse egg mixture evenly to the muffin cups.
Bake at 350F for 25 minutes or until the eggs are set and are starting to lightly brown. The egg muffins will deflate after being removed from the oven.
Let cool for a few minutes before removing the egg muffins from the muffin pan. Enjoy!