I've used good quality sandwich bread, but day old focaccia bread, french bread or ciabatta bread or buns works wonderfully as well. For cheese Iv'e used pepper jack, Asadero, Muenster, Cheddar, I do prefer a white melting cheese.
Slice tomato(es) and cook over low heat in a non stick skillet with a tsp of olive oil for about 10 min. turning once.
Spray one side of bread with spray oil, spread Thai chili sauce on other side. You want the Thai chili sauce on the inside of your sandwich, place cheese on on Thai sauce.
Place tomatoes on next.
Then onion slices and cilantro.
Finish off with more cheese. Toast on griddle, grill or in skillet till bread is browned and cheese is melted.