Wash the spinach thoroughly and roughly chop it. Squeeze out as much excess moisture as possible to prevent sogginess in the muffins.
Preheat your oven to 180°C (350°F) and line a muffin tin with paper liners or lightly grease it.
In a large mixing bowl, whisk together the eggs, olive oil, and milk until the mixture is smooth and slightly frothy, about 30 seconds.
Add the flour, baking powder, salt, and pepper to the wet ingredients. Gently fold everything together until just combined; avoid overmixing to keep the muffins tender.
Stir in the chopped spinach and crumbled feta cheese, folding gently until evenly distributed throughout the batter.
Using a spoon or ice cream scoop, evenly divide the batter among the muffin cups, filling each about three-quarters full.
Bake in the preheated oven for 20-25 minutes, until the muffins are golden on top and a toothpick inserted into the center comes out clean.
Remove the muffins from the oven, and let them rest in the tin for about 5 minutes to set. Then transfer to a wire rack to cool slightly.
Serve the muffins warm or at room temperature, perhaps with a drizzle of olive oil or a dollop of yogurt for extra flavor.
