Drain the oil from the canned tuna by using a strainer.
In a bowl, mix the tuna, mayonnaise, salt, and pepper together.
Spread butter on one side of a slice of bread.
Place the bread buttered side down on a pan.
Layer cheese, tuna mixture, more cheese, and then another slice of bread on top.
Spread butter on the outer side and cook over medium-low heat until both sides are golden brown.