If using bamboo skewers, soak skewers in water for at least 20 minutes. This will prevent the skewers from burning on the grill.
Heat vegetable oil in medium saucepan. Add onions and saute until soft and translucent, about 7 minutes.
Add garlic and ginger and saute until fragrant, about 1 minute.
Add remaining ingredients and simmer for 10 Minutes. Cool sauce completely.
Reserve half of the sauce for basting.
Place shrimp in a resealable bag and pour remaining sauce over shrimp.
Close bag and knead to ensure all shrimp is coated in sauce. Refrigerate for 1 hour to overnight.
Remove shrimp from marinade and throw marinade away.
Thread onto the skewers.
Spray grill lightly with cooking spray and preheat grill on medium high.
Place shrimp on grill and grill until well browned on one side, about 5 – 7 minutes.
Turn and baste with sauce.Grill another 5 to 7 minutes. Turn and baste again.
Continue grilling until well caramelized and the shrimp is cooked through.
Remove and serve with reserved sauce.