In a mixing bowl, combine the shredded chicken with ranch dressing, ensuring the chicken is well-coated. Add in the crumbled bacon, diced tomatoes, finely chopped red onion, and chopped cilantro, mixing gently to combine.

Place one flour tortilla on a clean, flat surface, and sprinkle a generous layer of shredded Mexican cheese across half of the tortilla. Spoon a portion of the chicken mixture over the cheese, then add another light layer of cheese on top.

Preheat a non-stick skillet over medium heat and add a pat of butter, allowing it to melt until bubbling.

Carefully place the folded quesadilla in the skillet, cooking for 2-3 minutes. Flip the quesadilla and continue cooking for an additional 2-3 minutes.

Once cooked, remove the quesadilla from the skillet and let it rest for a minute. Slice into wedges and serve warm.