Slice leftover pork into small strips,then set aside.
Cut pepper and onion into small strips.
Heat oil. After oil heated, saute peppers and onions until still slightly browned.
Add pork to the onions and peppers just until pork is warm. Then transfer all to a plate and set to side.
Heat large skillet on med to med high. Take tortilla shell and spray 1 side with cooking spray. Lay half of shell on pan. Add 1/4 of meat mixture on shell. Pour desired amount of BBQ sauce over mixture, then add 1/4 of cheese. Fold other half shell over and heat until shell slightly browned. Flip over and brown other side. Repeat until all 4 quesedillas are done.