This classic tuna melt can be made in a frying pan! If you like a little more texture to your toastie, it also works well with a tablespoon of finely diced celery folded through the filling.
Top tuna with cheese, packing it on generously, and slide sandwiches under broiler. Broil until cheese melts and bubbles, 4-5 minutes. Remove tuna melts from broiler and serve immediately.