Preheat oven to 400 degrees F. Rinse and pat dry the fish. Julienne or slice onion and zucchini. Toss the vegetables with half of the oil. Spread half of the vegetables on the bottom of the dish, top with fish fillet and drizzle it with remaining oil. Then top fish with the rest of the vegetables. Sprinkle lemon juice and herbs over the mixture plus a couple of grinds of black pepper, if desired. Cover with foil and bake about 15 minutes or until fish is no longer translucent and vegetables are tender.