In a large mixing bowl, combine the shredded cooked chicken with ranch dressing, ensuring each piece is well-coated. Add crumbled bacon, diced tomatoes, finely chopped red onion, and fresh cilantro.

Place a nonstick skillet over medium heat and add 1 tablespoon of butter, allowing it to melt completely.

Lay one flour tortilla in the skillet. Sprinkle half of the Mexican cheese blend on one side of the tortilla. Spoon a generous portion of the chicken mixture evenly over the cheese, and top with more cheese.

Fold the tortilla in half, pressing gently with a spatula. Cook for 2-3 minutes until golden brown. Flip and cook another 2-3 minutes.

Remove the quesadilla from the skillet and let it rest on a cutting board for 1 minute. Cut into wedges.

Serve hot, alongside salsa, sour cream, or guacamole.