Preheat a flat griddle or a large skillet over medium heat.
Spread marinara sauce on half of the tortilla. Sprinkle with shredded mozzarella cheese, and any other toppings of your choice. Add another layer of mozzarella over toppings. Fold tortilla over.
Spray griddle with cooking spray and cook quesadilla for 2-3 minutes per side, or until browned. Remove to a cutting board and allow the quesadilla to cool for a few minutes. Cut into triangles and serve.