Add the drained tuna, finely chopped celery, red onion, mayonnaise, paprika, cayenne pepper, and lime zest to a bowl and mix well.
Heat a large non-stick skillet/frying pan over medium heat and add the butter.
Place the tortillas on a clean, flat surface. Sprinkle the cheese evenly onto each one.
Spread the tuna mixture evenly over one-half of each tortilla wrap, leaving a small border around the edge and fold the other half of the tortilla over to create a half-moon shape.
Carefully place one of the tortilla wraps open and facing upwards in a skillet/frying pan and cook for about 1-2 minutes until the cheese has melted.
Then lift the cheese-only side and fold in half. Continue to cook for 1-2 more minutes until golden brown on each side, pressing down with a spatula or slotted turner to allow some cheese to ooze out of the edges and crisp up in the pan.
Remove the quesadilla from the skillet/frying pan and let it cool for a minute before slicing in half or into wedges.
Serve immediately with your favourite dipping sauce, such as salsa, sour cream, or guacamole.