Sometimes I'll add raw cucumbers at the end; sometimes I'll cut the onions into rings and grill them. And if you have leftover steak, just slice it, toss it briefly on the grill, and use." ...
Cut your chosen bread in half and toast on both sides either on a grill pan or under the broiler. Spread with butter and loads of mustard. Pile on the onions and slice the steak before loading ...