Shredded cooked chicken, mortadella, cheese and lettuce between slices of sandwich bread, pressed until the cheese melts. Four sandwiches in about ten minutes.
Anything else goes in: tomato, mushrooms, avocado, whatever is in the fridge. The one thing worth keeping is the mortadella, which is what makes this a Colombian sandwich rather than a generic one. Butter the outside of the bread, not the inside, if you want it to toast rather than steam. If you are cooking it in a skillet with no press, put a second pan on top to weigh it down: the point is contact with the heat, which is what gets the cheese to melt before the bread burns.