Combine the teriyaki, ginger, garlic, sugar, sesame oil and sesame seeds in a bowl. Add the fish, cover and marinate for 10-20 minutes.
Trim the ends off the zucchini and quarter lengthways. Heat a non-stick frying pan over a high heat and add the oil. Add the zucchini and cook for about 2 minutes, until they begin to colour. Remove to a warm plate.
Remove fillets from marinade, reserving marinade.
Return the pan to the heat, add the Trevally fillets, and cook for 1-2 minutes, until the edges have turned opaque. Turn the fillets, add the zucchini and the reserved marinade and cook for a further 1-2 minutes, adding a few teaspoons of water if the marinade begins to caramelise.
Arrange the zucchini on plates, top with fillets and garnish with green onion. Serve with steamed rice.