Preheat your oven to 350°F and lightly grease a muffin tin with the olive oil.
In a small skillet over medium heat, cook the ground turkey and diced bell peppers until the turkey is browned and the peppers are slightly softened.
Roughly chop the fresh spinach and add it to the skillet for 30 seconds just until wilted, then remove from heat.
In a medium bowl, whisk together the large eggs, liquid egg whites, sea salt, black pepper, and garlic powder until well combined.
Distribute the turkey and vegetable mixture evenly among the muffin cups.
Pour the egg mixture over the vegetables in each cup, filling them about three-quarters of the way full.
Sprinkle the crumbled feta cheese over the top of each muffin.
Bake for 20-25 minutes, or until the eggs are set and the tops are lightly golden.
Allow the frittatas to cool for 5 minutes before removing them from the tin to serve or store for meal prep.