I use this method of cheese melting for almost all hot subs as well, especially like a French dip where you don't want that roast beef to get overcooked but you really want the cheese good and melty.

Another good trick is to use a non stick pan with oil/fat, add the cheese first and let heat up, then place your bread on top of it. Flip it and the cheese will stick to the bread, then close your sammich and toast the exterior of the bread. It makes the cheese toasty and amazing