Wash the fish, divide into 4 portions and sprinkle with lemon juice. Clean, wash and roughly grate the zucchini. Blanch briefly in boiling salted water and drain. Put the fish fillet also in boiling salted water and let it simmer for about 8 minutes.
Mix 1/4 litre water with the hollandaise powder and bring to the boil while stirring. Stir in butter in flakes and add the herbs. Season to taste with salt and pepper if necessary. Put the zucchini in an ovenproof dish and season with pepper.
Place drained fish on top. Cover with the herb hollandaise sauce and bake briefly under the hot grill of the oven. Serve garnished with lemon and dill. Baguette tastes good with it.