In a large bowl, combine the cooked chicken, crumbled bacon, ranch dressing, shredded cheeses, salt, pepper, and optional seasonings. Mix until evenly coated.
Lay tortillas flat on a clean surface. Spread the filling evenly over one half of each tortilla.
Fold tortillas over to close.
Heat a skillet over medium heat and add butter or oil.
Cook each quesadilla for 2–3 minutes per side until golden brown and crispy, pressing gently with a spatula.
Remove from heat, rest for 1 minute, then slice and serve warm.