Clean, wash and cut the zucchini into large cubes. Wash and clean the tomatoes and carve them crosswise. Season with salt and pepper. Wash fish fillets, dab dry, season with salt and pepper.
Put 1 salmon and 1 cod fillet each with 2 tomatoes in an ovenproof dish. Sprinkle with about 1/2 of the lime juice. Sprinkle zucchini over it. Heat 1/8 litre water. Stir in sauce powder and bring to the boil.
Stir in the rest of the lime juice. Cut butter into cubes and stir into the sauce. Season with salt and cayenne pepper. Spread the sauce on the fish fillets and bake in the preheated oven (electric range: 200 °C/ gas: level 3) on the lowest rack for 8-10 minutes.
Cover with aluminium foil if necessary. In the meantime, cut the olives into slices. Sprinkle olives on the fish pan and garnish with basil.