Cut the green onions into small pieces and slice the long onion into thin strips. Soak the long onion strips in water and drain well.

Cut the amberjack into bite-sized pieces and season with salt and pepper. Coat the pieces evenly with potato starch.

Heat sesame oil in a frying pan over medium heat. Add the amberjack and cook until both sides are golden brown and cooked through. Remove excess oil with a paper towel, then add the sauce ingredients and simmer until coated.