Cut the salmon into small chunks. Dice all the vegetables (asparagus, carrot, pepper, leek and sprouts) and plunge into boiling water for a few minutes (they must remain al dente). Cool in a bowl of iced water and drain.
Soak the sheets of rice paper in a bowl of just tepid water for 2 min. and then spread on a clean dry tea towel. Cut in half and arrange a little salmon and some vegetables on the end of each sheet. Then roll up, seal with water and trim off the ends. Put to one side.
Add the chopped garlic sprouts and the sprig of thyme to the stock. Bring to the boil and drain. Season with salt and pepper as required.
Serve two cannelloni per plate. Decorate each with half a teaspoon of ikura and, just before bringing to the table, pour over the hot stock.