In a small bowl, whisk together soy sauce, oyster sauce, ginger, rice vinegar, brown sugar, garlic, sesame oil, Sriracha and pepper, to taste.
Thread salmon, pineapple, red onion and zucchini onto skewers. Brush soy sauce mixture onto the skewers and let sit for 10-15 minutes.
Preheat grill to medium high heat. Add kabobs to grill, reserving the marinade, and cook, turning occasionally, until salmon is opaque throughout and vegetables are tender, about 5-7 minutes.
Add reserved marinade to a small saucepan over medium high heat. Bring to a boil; reduce heat and simmer until reduced by half, about 5-6 minutes.
Serve kabobs immediately with reserved marinade, garnished with cilantro, if desired.
Notes
*Cooking time will vary depending on the size and thickness of the salmon and/or vegetables.