My recipe for grilled cheese:
Due to lactose intolerance I use daiya cheddar slices, put a thin coating of mayo on one side of each slice. Throw them mayo side down into a nonstick pan then put the pan on the burner turned to medium. As soon as they get gooey quickly scrape em up and put them between slices of bread. Then toast the sandwich in the pan with butter like normal.
Depending on the amount of mayo and cook time the cheese may or may not stay gooey long enough. I'm still perfecting it.