Soak skewers in water for at least 20 minutes. This will prevent the skewers from burning on the grill.
Heat olive oil in medium saucepan. Add onions and sauté until soft and translucent, about 7 minutes.
Add garlic and ginger and sauté until fragrant, about 1 minute.
Add remaining ingredients and simmer for 10 minutes; Remove from heat and cool sauce completely.
Place chicken in a bowl and pour half of the sauce over chicken; reserve remaining sauce. Mix well to ensure all chicken is coated in sauce. Set aside for 20 minutes.
Remove chicken from marinade. Thread chicken onto the skewers.
Spray grill lightly with non-stick spray and preheat a grill on medium heat. (Alternatively, cook in a 400°F oven to an internal temperature of 160°F.) Place chicken on grill and grill until well browned on one side, about 5 minutes. Turn chicken and brush with marinade. Grill another 5-7 minutes. Turn and brush again.
Continue grilling until well caramelized and the internal temperature reaches 160°F.
Remove chicken and drizzle with reserved sauce and dinner rolls. Garnish with scallions.