Spread a thin layer of mayonnaise and mustard on each piece of bread and set 4 slices aside. Slice the chicken breast into thin pieces and place 1 slice of cheese, a few slices of chicken on the bread and top with a little rocket and then another slice of cheese. Top with remaining bread. Heat your grill or grill pan and brush both sides of the sandwich generously with butter or oil. Grill for about 5 minutes or until toasted and cheeses has melted. If using a grill pan gently turn after 1 – 2 minutes. Tip: You can add other filling too like slices of capsicum, tomato or grilled zucchini for variety.