For the special sauce: Add ingredients to a bowl then stir to combine.
Add cooked ground beef to a bowl then add ketchup and mustard to taste. You'' want the mixture to be more saucy vs dry.
Heat a flat griddle or skillet over medium heat then spray with nonstick spray. Place a tortilla onto the skillet then sprinkle on a thin layer of cheddar cheese followed by the ground beef mixture. Add desired toppings then sprinkle on another thin lay of cheese and place a tortilla on top.
Once the tortilla on the bottom has browned, flip then continue cooking until the second tortilla has browned. Remove quesadilla to a cutting board then let cool for 5 mins before slicing with a pizza cutter. Serve with special sauce.