Heat the oil in a saucepan, sauté the onion cubes and peas. Deglaze with the broth and cream, simmer for about 10 minutes. Puree fine, strain through a sieve, put back in the saucepan. Heat, add wasabi and rice vinegar, season with salt and pepper. Depending on your taste, the amount of wasabi can be increased.
Clean and wash the spring onions and cut into rings.
Serve the soup in preheated plates, each with a slice of salmon, a few spring onion rings and possibly some trout caviar.