This turned out to be quite messy. But it was so simple in my head that I decided to whip this one up for lunch.
Leftover tuna in a can flaked and mixed with finely chopped garlic and onion. The mixture was seasoned with pepper, herbs of your choice, I used Italian mixed herbs here, and a squirt of mustard (I ran out of mayo). The bagel was spread generously with cream cheese before piling up the tuna on. Then grated cheese was sprinkled generously over the pile. This was where messy started. Cheese all over the counter and more cheese and tuna flake all over the counter as it was being transferred into the toaster oven for a quick bake. It's time to eat when the cheese melted and turned bubbly brown.
Tuna cheesy melt became tuna cheesy mess. Tasty nonetheless, if I may add.