You will need some things to make this happen. If you have some stale bread and a clothing iron in your closet, you are halfway there already.
-iron (it’s not made for cooking but it works)
-aluminum foil (remove before consuming)
Do what you need to do to create the goodies in between the bread. This includes mixing up the mayo and tuna fish. Have a layer of cheese in between the tuna and bread. Be sure to have cheese-to-bread contact on both sides or else the cheese will have difficulty melting. Wrap sandwich in tinfoil. Notice there is no need for oil or butter.
Put iron on hottest setting and let it sit on top of the foil for 5 minutes. You may want to peek inside before the 5 minutes to make sure it is getting cooked properly. Carefully turn the half-melt over to singe the other side.
The final product will sure impress your hungry friends, the debt-ridden neighbor, and the people you know who have a fear of stoves. If you are higher maintenance, you can throw some garlic, celery, or chopped spinach or tomato in the mixture before ironing. If you like to keep things simple, convert your grilled cheese into ironed cheese.