Organise a 'Ready Steady Cook' night. Provide the same ingredients for each group - and see how they get on! (It helps if each group has their own kitchen.) Set a time limit, and offer points for categories (presentation, taste, originality). They can do as many courses as they wish.
Invite a church member who is not British to make traditional food from their home country (Swedish meatballs? French crepes?) with your group. Theme the evening around their country, or even have a 'world night'.
Hold an end of term prom night that includes a banquet. Print tickets, make the dress formal and let the cheesy dancing begin.