Warm skillet over medium heat.
Place one tortilla onto skillet and sprinkle with half of the cheese.
Lightly break up tuna with juices and place evenly over cheese.
Top with diced jalapeño and an even layer of sliced avocado.
Sprinkle with remaining cheese.
Place the second tortilla on top and cook until bottom tortilla is golden brown and crispy.
Carefully flip the quesadilla to cook the other side and until cheese is melted.
Remove from pan, let cool for one minute before cutting.