1combine onion and vinegar in a bowl let stand for 5 minutes.
2Drain the vinegar for another use.place 2 tortillas in a large non stick skillet over medium heat warm about one minutes then flip pull tortollas up the edges of the pan so they are no longer over lapping.
3Working on the half each tortilla sprinkle cheese cover with 2 slices of chicken and top with onion slice.
4Fold the tortillas in half press gently with spoon to flattern and cook until the cheese start to melt about 2 minutes.
5Flip and continue cooking until the second side is golden 1 to 2 minutes .
6Transfer to the plate and cover with foil to keep warm makes two and more Quesadillas with the remaining indregients serve warm.