In a bowl, whisk together the soy sauce, maple syrup, rice vinegar, sesame oil, garlic, ginger, and red pepper flakes.
Reserve 1/4 cup of the marinade in a separate bowl for the glaze.
Place the salmon in a shallow dish and pour the remaining marinade over it.
Let the salmon marinate at room temperature for 30 minutes.
Preheat the grill to medium-high heat (400-450F).
Clean and oil the grill grates thoroughly.
Remove the salmon from the marinade, letting excess drip off.
Place the salmon skin-side down on the hot grates.
Grill for 4-6 minutes until the skin is crispy and releases easily.
Flip the salmon and brush the skin side with the reserved marinade.
Continue grilling for 3-5 minutes, basting occasionally, until internal temperature reaches 125F for medium-rare.
Let the salmon rest for a few minutes.
Garnish with the sliced scallions.
Serve over rice to catch the extra glaze.