Season chicken breasts with a little salt and black pepper. Place them in a resealable plastic bag.
Chop green onion and reserve 2 tablespoons of green portion for garnish. Chop chili and also reserve as garnish.
Combine all marinade ingredients in a medium bowl, until blended through. Divide mixture in half. Pour half into the bag with chicken. Make sure all four breasts are well coated. Seal bag and place into refrigerator for 2-12 hours. Reserve the other half in the fridge for later.
Preheat grill for medium high heat.
Place reserved marinade mixture into a saucepan and bring to a heavy simmer on high heat. Reduce heat to medium low and simmer for 6-8 minutes, stirring occasionally. Watch for burning and reduce heat to low if needed. Once sauce has thickened enough to coat the back of a spoon (with a syrup-like appearance), remove from heat, cover and set aside. Re-warm if needed.
Remove chicken breasts from bag and place on grill. Cook for 6-8 minutes per side or until the internal temperature at the thickest part of breasts reaches 165 degrees F. Reduce heat to medium if flare-ups occur, or move to cooler part of the grill and finish cooking over indirect heat.
Once cooked through, remove chicken from heat and place onto a cutting board.
Slice each chicken breast and set over rice (or noodles), top with warmed teriyaki sauce and garnish with reserved green onion and sliced chili.