2. In a bowl, mix the drained tuna with mayonnaise.
3. Spread butter on one side of each bread slice.
4. Place one slice of bread, buttered side down, on the panini press. Add a slice of cheese, the tuna mixture, another slice of cheese, and top with the second slice of bread, buttered side up.
5. Close the panini press and cook for about 5 minutes, or until the bread is golden and the cheese is melted.