Prepare marinade: Combine soy sauce, sugar, garlic, green onion, and oil; set aside. Place sesame seeds in a medium frying pan and stir over medium heat until they begin to brown (they brown quickly, so watch). Add to soy sauce mixture.
Lay fillets skin down in a single layer in a pan with raised sides. Pour soy mixture over fillets. Let sit for a moment, then turn fillets so they are flesh side down. Cover and refrigerate for 30 minutes.
When ready to grill, remove from marinade and place bass on oiled grill over ashen coals, skin side touching the grill; grill for 3 - 4 minutes on one side only. (Do not turn fillets or they will fall apart). Baste fillets with marinade every minute or so until done. Use a greased spatula to transfer fish to serving platter.