In a skillet over medium heat, pour 2 tablespoons of olive oil and let it warm for about 1 minute. Add 1 cup of chopped onions and 2 cloves of minced garlic, stirring frequently for 2–3 minutes until the onions become translucent and fragrant.

Next, add 4 cups of fresh spinach to the skillet with the sautéed onions and garlic. Stir occasionally as the spinach wilts, taking about 2 minutes. Season with salt and black pepper, mix well, and set aside.

Lay a large flour tortilla flat on a clean surface. On one half, spread a quarter of the spinach mixture, followed by a sprinkle of crumbled feta and shredded mozzarella cheese. Fold over to create a half-moon shape.

Heat the skillet again over medium heat. Add a pat of butter, and when melted, place the folded quesadilla in the skillet. Cook for 3–4 minutes until golden brown and crispy. Flip and cook for another 3–4 minutes until the cheese is melted.

Once both sides are browned and the cheese is melted, remove from the skillet and let cool for 1 minute. Slice into wedges for serving.