01 -
Preheat the oven to 350°F. Grease a 12-cup muffin tin very well with olive oil spray or olive oil, including the upper rim of each cup.
02 -
If using fresh spinach, wilt it in a skillet for 1-2 minutes, then cool slightly and squeeze out moisture. If using frozen spinach, thaw it and squeeze it dry in a clean towel.
03 -
In a large bowl, whisk the eggs, milk, baking powder, oregano, salt, and pepper until smooth and lightly foamy.
04 -
Fold in the spinach, feta, green onion, red bell pepper, and parsley until evenly distributed.
05 -
Divide the egg mixture evenly among the prepared muffin cups, filling each about three-quarters full.
06 -
Bake for 18-22 minutes, until the tops are puffed and the centers are set. Rest in the pan for 5 minutes, then loosen the edges and transfer to a rack.