01 - Preheat oven to 350°F. Lightly grease a 6-cup muffin tin with olive oil or nonstick spray.
02 - In a mixing bowl, whisk together eggs and milk until well combined. Season with salt, pepper, and oregano if using.
03 - Stir in chopped spinach, bell pepper, green onion, and crumbled feta.
04 - Divide the mixture evenly among the prepared muffin cups, filling each about 3/4 full.
05 - Bake for 18–20 minutes, or until muffins are puffed and the centers are just set.
06 - Let cool for 5 minutes before removing from the tin. Serve warm or at room temperature.