1. Preheat your oven to 375°F (190°C). Generously grease a 12-cup standard muffin tin with non-stick cooking spray (or use silicone muffin liners for guaranteed easy removal).

2. Sauté the Veggies (Crucial Step): Heat the olive oil in a skillet over medium heat. Add the diced onion and cook for 3-4 minutes until soft.

3. Add the chopped fresh spinach and garlic. Cook for another 2 minutes until the spinach is fully wilted and most of the liquid has evaporated. (If using frozen/thawed spinach, just stir it in with the onions to warm through). Remove from heat.

4. Whisk the Eggs: In a large bowl, whisk together the eggs, milk, salt, pepper, and oregano until smooth and frothy.

5. Assemble: Distribute the cooked spinach and onion mixture evenly among the 12 muffin cups.

6. Sprinkle the crumbled feta cheese evenly over the vegetables in each cup.

7. Pour the egg mixture into the cups, filling them about ¾ of the way full. (Do not overfill, as they will puff up while baking).

8. Bake for 20–25 minutes, or until the muffins are puffed, golden on top, and the centers are set (not jiggly).

9. Cool: Remove from the oven. Let them cool in the pan for 5 minutes before running a butter knife around the edges to pop them out. Serve warm.