01 - Preheat the oven to 350°F. Lightly grease a 12-cup muffin tin or line with silicone muffin liners.
02 - Heat olive oil in a skillet over medium heat. Add the chopped spinach and sauté for 2 to 3 minutes until fully wilted. Remove from heat and let cool slightly.
03 - In a large mixing bowl, whisk together the eggs, milk, salt, pepper, and dried oregano until well combined.
04 - Fold the sautéed spinach, chopped sun-dried tomatoes, and crumbled feta cheese into the egg mixture. Stir gently until evenly distributed.
05 - Divide the mixture evenly among the prepared muffin cups, filling each about three-quarters full.
06 - Bake for 18 to 22 minutes, or until the egg muffins are set in the center and lightly golden on top.
07 - Allow the muffin cups to cool in the tin for 5 minutes before removing. Serve warm or at room temperature.