Heat 1 tablespoon olive oil over medium heat in a large skillet.
Add onion; cook and stir onions until softened about 5 minutes. Stir in bacon pieces and brown sugar, and cook until bacon pieces are crisp.
Remove from skillet.
Spread 1/4 cup barbecue sauce on one tortilla.
Sprinkle with 1/4 of the bacon and onion mixture, 1 tablespoon cilantro, and 1/2 cup Cheddar cheese. Top with a tortilla.
Heat 1 teaspoon olive oil over medium heat in a large skillet.
Place the uncooked quesadilla in the skillet. Cook on one side until browned and crisp, about 3 minutes. Flip, and cook on the other side until the cheese is completely melted, about 2 minutes more.
Remove to a paper towel lined plate to cool. Repeat with remaining six tortillas. Slice into quarters using a sharp knife or kitchen scissors when cool enough to handle.