Preheat the grill. Mix together the onion, tomato, chilli, green pepper, coriander and sweet chilli sauce or tomato ketchup. Season with pepper.
Toast one side of the bread under the grill, then layer the vegetable mix over the untoasted side of the bread. Flash under the grill for 3 minutes, so the onion softens slightly.
Top with the cheese and cook until golden and bubbling. Serve immediately.