Dice the bacon. Fry the diced bacon in a dry pan over medium heat until crispy. Remove from pan.
Dice the onion. Saute the diced onions in a dry pan over medium heat until softened and browned. Remove from heat. Stir in the shredded chicken, cooked bacon and ranch dressing.
Remove the mixture into a separate bowl and wipe the pan clean.
Coat the pan with nonstick cooking spray. Lay one tortilla in the pan and spread half of the chicken mixture on top. Sprinkle half of the grated cheese evenly over the chicken mixture. Place the other tortilla over top.
Turn the burner on to medium heat and cook until the bottom tortilla is golden brown. Carefully flip it over. Watch for the bottom tortilla to turn golden brown and the cheese to melt.
Remove the quesadilla from the pan onto a work surface. Slice into triangles.