Dice rotisserie chicken, grate cheese, and dice jalapeno peppers. (You can choose to discard jalapeno seeds or leave them in to make it spicier.) Combine chicken, cheese and jalapenos in a mixing bowl and mix until evenly mixed throughout.
Preheat a cooking pan over medium heat and grease it lightly with some cooking spray.
Place 1 tortilla in the cooking pan and spread a third of the filling all over the tortilla. Cover with another tortilla and and spray the top with some cooking spray.
Cook until cheese starts to melt and bottom tortilla is browned. Flip on the other side and cook until that side is browned as well.
Repeat with remaining tortillas and filling.
Note: if available, you can cook more than one quesadilla at a time on a griddle. Note: you can keep cooked tortillas warm in the oven heated to 200°.