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 wilted. Remove from heat and let cool slightly.
03 - In a large bowl, whisk together the eggs, milk, salt, pepper, and oregano until well combined.
04 - Fold the sautéed spinach, sun-dried tomatoes, and crumbled feta into the egg mixture. Stir gently to distribute evenly without overmixing.
05 - Divide the mixture evenly among the prepared muffin cups, filling each about three-quarters full.
06 - Bake for 18 to 22 minutes until the egg muffins are set and lightly golden on top. A toothpick inserted in the center should come out clean.
07 - Let the muffin cups rest in the tin for 5 minutes before removing. Serve warm or at room temperature.