Spinach and Feta Quesadillas

1 Tbsp Olive Oil
1/2 small Onion (finely chopped)
10 oz package Frozen Spinach (thawed and squeezed dry)
6 oz Feta (crumbled)
1/4 cup Kalamata or Other Black Olives (pitted and chopped)
4 10-inch Flour Tortillas

Warm oil in a medium skillet over medium-high heat. Add onion and cook, stirring, until softened, about 3 minutes. Stir in spinach and cook, stirring, until heated through, 2 to 3 minutes longer. Transfer to a bowl and stir in cheese and olives. Spread 1/4 cup of cheese mixture over 1/2 of each tortilla. Fold to cover; press lightly to seal. Place a large skillet over medium-high heat. Cook quesadillas one at a time in skillet, turning once, until gloden on both sides and cheese is melted, about 6 minutes total for each. Serve immediately.