Trim the duck breast and pan-fry fat side down first without adding any oil to the pan. When the duck is sealed from both sides, add the cherry tomatoes to the pan and continue cook in the oven for a further 9 minutes in the oven at 180`c. Meanwhile, slice the onions and cook in a pan with the butter and sugar until well browned and caramelized. Add the cranberry sauce to the pan and remove off the heat. Cut the Rye bread into approximately 4cm squares and toast lightly under a hot grill. To serve, place 3 pieces of toasted rye bread on each plate topped with the onion marmalade on each piece. Cut the duck in thin slanting slices and skewer onto long kebab sticks with the cherry tomatoes. Insert into the marmalade toast and serve.