To make the teriyaki, whisk together the brown sugar, sesame oil and soy sauce in a medium bowl. Stir in the ginger and garlic. Use 1/2 of the teriyaki to marinate the salmon. Reserve the other half. Refrigerate the marinating salmon for 2 hours.
To make the slaw, combine the broccoli, cabbage, carrots, bell pepper and onion in a medium bowl. Stir in the mayonnaise and Sriracha. Cover and refrigerate.
Prepare the grill for direct grilling at 500°F.
Remove the salmon from the marinade. Discard the marinade and pat the salmon dry with paper towels. Place the salmon in the direct grilling zone with the skin side up. Cook the salmon halfway through, about 5 minutes. Flip the salmon over so the skin side is down. Brush with the reserved teriyaki. Repeat brushing every minute or so until the salmon is cooked through, about 4 minutes on the second side. The salmon is cooked when the meat flakes cleanly under gentle pressure. Slide your spatula between the meat and the skin to remove the fish from the grill, leaving the skin behind.
Quickly grill each tortilla on one side.
Break the fish into smaller pieces and split it among the tortillas. Finish the tacos by topping each with a little broccoli slaw.
