Step 1Combine the mustard, brown sugar, vinegar and one-fourth cup mayonnaise to make a sweet mustard sauce. Set aside.
Step 2Pulse the salmon in a food processor to chop coarsely.
Step 3Mix the salmon, onions, capers, parsley, salt, pepper and the remaining mayonnaise in a medium bowl. Add one-fourth cup panko bread crumbs.
Step 4Form the mixture into six equal patties, then lightly coat the patties with the remaining panko.
Step 5Heat the olive oil in a large skillet over medium heat and add the salmon patties. Cook until golden brown on both sides, about 7 minutes total. Serve on toasted rolls with the sweet mustard sauce.