Wash the salmon, dab dry, cut into cubes and sprinkle with lemon juice. Shrimps wash and pat dry. Clean and wash spring onions and cut them into diagonal rings. Heat oil in a pan.
Fry the salmon and prawns for about 4 minutes, season with salt and pepper. Remove salmon and prawns and keep warm. Pour fish stock and prosecco into the frying fat and bring to the boil. Stir in lobster paste.
Refine with cream and season with salt and pepper. Cook the pasta in plenty of boiling salted water for about 5 minutes. Heat butter and fry spring onions for about 3 minutes. Arrange spaghettini with salmon, prawns, spring onions and the prosecco sauce on small plates or platters.
Place 1 teaspoon of trout caviar on each noodle and serve.