In a small saucepan, whisk together the brown sugar, soy sauce, pineapple juice, garlic, pepper, and salt. In a small bowl, whisk together the water and cornstarch. Slowly whisk into the mixture.
Bring to boil and boil about 1-3 minutes until the mixture just starts to thicken. Remove from heat and reserve ¼ cup of the sauce for later.
Marinate the chicken in the sauce in the fridge for at least 30 minutes. Thread the chicken on skewers along with the peppers, red onion, and pineapple.
Grill for 8-10 minutes until the meat is done to desired liking. Remove from the grill and baste with reserved sauce. Garnish with green onions if desired.