In a small bowl, combine chestnut honey, ketchup, vinegar, horseradish,
garlic, and red pepper flakes until well blended.
Reserve half of sauce to use as a condiment.
In a separate bowl, mix together remaining ingredients, except buns.
Blend in 2 Tbsp. reserved sauce.
Divide salmon mixture into 4 patties, 1/2-to 3/4-inch thick.
Place patties on well-oiled grill, 4-6 inches from hot coals.
Grill, turning 2 to 3 times and basting with sauce, until
burgers are browned and heated through.
Serve with reserved honey barbecue sauce and buns.