4 large (10-inch) whole wheat tortillas
Fresh spinach leaves, chopped (about 2 cups)
Diced red onion (about ½ cup)
Roasted red peppers, chopped
Sliced black olives
Mozzarella cheese, shredded (about 1-1½ cups)
Crumbled feta cheese (about 2/3 cup)
Oregano (dried or fresh)
Red pepper flakes
Place tortillas on a work surface. Very lightly brush one side of each tortilla with olive oil and flip over so the oiled side is facing down. Sprinkle the chopped spinach leaves over half of each tortilla, leaving a small rim around the edge. Layer in a similar fashion with red onion, roasted red pepper, tomatoes, olives, cheeses, oregano, and red pepper flakes as desired. Fold over the bare half of each tortilla, enclosing the fillings.
Warm a skillet or grill pan over medium-high heat and if needed, lightly oil the cooking surface. Carefully place assembled quesadillas in the pan and cook, turning once, until each side is golden brown and the cheese is melted. Slice into triangles and serve warm.