In a mixing bowl, combine ½ cup of shredded mozzarella, ½ cup of crumbled feta, 1 cup of chopped fresh spinach, 1 diced small tomato, ¼ cup of thinly sliced red onion, and ¼ teaspoon of black pepper. Stir until well incorporated.

Lay one flour tortilla flat. Place one-fourth of the filling onto one half, then fold the tortilla to create a half-moon shape.

Heat a non-stick skillet over medium heat for about 2 minutes. Add 1 tablespoon of olive oil, swirling to coat the skillet.

Place one quesadilla in the skillet and cook for 3 to 4 minutes until golden brown. Flip and cook the other side for an additional 3 to 4 minutes.

Remove and cool for a minute before slicing into wedges. Serve immediately.