Boil the prawns, rinse and let them cool.
Prepare the dill mayo by mixing it with the yogurt, chopped dill, salt and pepper.
Separate the sauce in two bowls.
To one of those bowls, add the chopped scallion.
Toast the bread.
Use the scallion mix to put on the base of the German rye bread and then asemble with the smoked salmon, radish, cucumber and both caviar colours.
Be careful because some caviar has too much salt, so make sure you use only the amount you need.
Mix the other bowl with the prawns and the assemble the toast by placing chopped lettuce between the bread and the prawn mix (this prevents the bread from becoming soggy).
Decorate with some more fresh fennel.
If you want to veganize this:
Prawn: cubbed tofu + seaweed.
Salmon: thinly sliced smoked tofu + seaweed.
Mayo and yogurt: choose a vegan alternative. Coconut yogurt should work fine, although a little bit sweeter, so add a hint of lemon and some salt.
If you are a vegetarian but don't eat soy, use egg instead of tofu.