Pat salmon dry and season with salt and pepper to taste.
In a bowl, combine hoisin sauce, rice vinegar, Sriracha hot sauce (if using), sesame oil, ginger, and garlic. Stir until blended.
Add salmon fillets and gently toss to fully coat. Marinate for about 20 to 30 minutes in the fridge.
Lightly grease a baking sheet or a cast iron skillet. Arrange salmon fillets in a single layer, spooning the marinade over fish.
Set oven rack to about 10 inches below heat source and turn broiler to high. Broil salmon for about 8 to 10 minutes or until the top is caramelized and fish easily flakes with a fork. Alternatively, grill fish over hot coals for about 4 to 5 minutes on each side, basting regularly with marinade.
Garnish with toasted sesame seeds, if desired. Serve hot.
Notes
Do not keep the salmon in the marinade for too long as the acids will break down the protein and make the texture mushy.