Clean the spinach and rinse thoroughly under running water to remove any dirt. Place the spinach in a skillet, cover with a lid, and cook for 10 to 15 minutes. Drain in a colander, then squeeze out all excess water by hand.

Beat the eggs in a bowl. Add salt, Parmesan cheese, and finally the milk. Add the chopped spinach and provolone cheese, then mix until everything is well combined.

Heat oil in a skillet. When it starts to sizzle, pour in the frittata mixture. Cover with a lid and cook. Flip the frittata using the lid and cook on the other side until done.