Rinse and top and tail the zucchini (courgettes).
Peel a strip of skin lengthwise from each about 1/2 inch (1.25 cm) wide.
Put the zucchini (courgettes) on a dish with 2 tablespoons of water.
Cover and microwave on HIGH for 7 minutes.
Remove the zucchini (courgettes) carefully with a spatula and leave to cool.
Put the salmon on a small dish.
Cover and microwave on HIGH for 2 minutes, then leave to cool.
With a teaspoon, carefully remove the pulp from the zucchini (courgettes) on the peeled side.
Leave a thin layer of pulp in the vegetable.
Salt the zucchini (courgette) shells and replace on the dish.
Remove the bones and skin from the salmon steaks.
Puree the flesh with the pulp from the zucchini (courgettes).
Mix together the egg yolk and the mustard.
Add salt and pepper.
Gradually add the oil in a thin trickle, whisking constantly until a thick mayonnaise is obtained.
Add the lemon juice and continue to whisk until it is incorporated.
Stir the mayonnaise into the salmon and zucchini (courgette) puree and add the chopped dill.
Taste and adjust seasoning.
Fill the zucchini (courgette) cases with this mixture.
Arrange on a serving dish and decorate with whole unshelled shrimp (prawns).