Toast the sandwich roll in a large skillet.

In the same skillet, cook the bacon.

Slice the half onion into strips and sauté with a little oil.

Remove the onion. Assemble the sandwich by adding the bacon first, then the onion.

Place the cheese slices in the skillet and let them melt slightly without fully detaching them from one end. When the cheese starts to melt, place it over the onion in the sandwich.