For avocado feta frittata, clean and wash the scallions and cut into fine rings. Squeeze the lemon. Cut the avocado in half, pit it and remove the flesh from the skin. Cut the avocado flesh into cubes, place in a bowl and immediately sprinkle with the lemon juice (see tip).
Whisk the eggs in a bowl with the milk and season with salt and pepper. Heat the olive oil in a non-stick frying pan over medium heat. Sauté the scallions in it for about 2 minutes.
Pour the egg-milk mixture over them and swirl to distribute until the bottom of the pan is completely covered. Let the egg mixture set for 2-3 minutes, then sprinkle the avocado cubes on top.
Crumble the feta cheese and spread evenly over the frittata. Cover the pan with a lid and continue frying the frittata over low-medium heat for 10 – 12 minutes, until the egg mixture is completely set.
Slide the frittata onto a cutting board and cut in half. Arrange the halves on two plates and serve the avocado-feta frittata immediately.