Mince all the salmon, then place half in a large sealable plastic bag and use a flat-surfaced meat pounder or a rolling pin to mash it. Place all the salmon in a large bowl and combine with the egg whites, mustard, bread crumbs, salt, and dill. Form 4 patties, each 3/4 inch thick. Place on a medium-hot grill and cook 4 to 5 minutes per side. (To cook on a stovetop, heat the olive oil in a grill pan over medium heat and cook the patties 5 minutes per side.) Top with Tangy Coleslaw, if desired, and serve on the brioche buns.