There is no shortage of companies in Brussels that provide catering services for anything you are organising.  From weddings and special celebrations to corporate buffets and lunches, these companies will lighten the organisational load no end!
Most caterers in Brussels by now offer personalised menus, whereby you can decide together what exactly will be served.  Although they will obviously suggest their specialities, and whatever foods are in season, this gives you the opportunity to personalise the buffet as you please.