In a small mixing bowl combine chicken, pineapple BBQ sauce and pineapple.
Take one tortilla and lightly spray one side with nonstick spray.
Flip evenly add the chicken/BBQ sauce and pineapple combo.
Add sliced onion then sprinkle with cheese.
Heat a skillet over medium heat.
Add the quesadilla to the skillet, the sprayed side down. Top with another tortilla.
I use a round glass pie dish to press down the quesadilla, this helps everything stick together in my opinion.
Let cook for about 3-4 minutes or until the bottom tortilla is browned. Spray the top tortilla with nonstick spray.
With a spatula, very carefully flip the quesadilla, some contents from the quesadilla may fall out but you can stuff them back in.
Cook on the other side 3 additional minutes, or until browned and crispy. I use the glass pie dish on this side as well to really press everything together.
Remove from heat and cut into 4 slices.