In a small bowl, combine soy sauce, honey, rice vinegar, ginger, garlic powder, and red pepper flakes to make the marinade.
Place salmon in a shallow dish and pour the marinade over it. Marinate for at least 30 minutes, or up to 2 hours.
Toss Brussels sprouts with olive oil, salt, and pepper.
Grill or broil salmon and Brussels sprouts for 5-7 minutes per side, or until cooked through.
In a small bowl, combine mayonnaise, Dijon mustard, honey, lemon juice, and garlic powder. Mix well to make the sauce.
Serve salmon and Brussels sprouts over rice or quinoa and drizzle with the sauce.