In a large skillet, heat the olive oil over medium heat. Add the chopped spinach and sauté for about 2-3 minutes until wilted.
Remove the skillet from heat and stir in the feta cheese, mozzarella cheese, garlic powder, onion powder, salt, and pepper until well combined.
Place one tortilla in the skillet over low heat. Spread a quarter of the spinach and cheese mixture evenly over half of the tortilla.
Fold the tortilla in half and cook for about 2-3 minutes on each side, or until golden brown and the cheese is melted.
Repeat with the remaining tortillas and filling.
Cut each quesadilla into wedges and serve warm with sour cream or salsa if desired.