Mix together mustard, honey, soy sauce, lime juice, rice wine vinegar, sesame oil, and minced garlic. Marinate salmon filet with the honey sauce for at least 30 minutes (preferably overnight).
When ready to cook, remove the salmon from marinade, pat it dry, and salt and pepper both sides. Brush a preheated grill with the grape seed oil and cook the salmon skin-side up for 4 minutes, then flip over and cook for another 5 minutes or until the salmon is just cooked.
While the fish is cooking, make the honey sauce. In a small saucepan, bring the marinade to a boil. Make a slurry with the cornstarch and water and add it to the heating sauce. Boil for 1 minute to cook and thicken slightly. Add a pinch of salt, then serve with the grilled salmon.