Salad with smoked red fish and green peas

Any red fish (smoked, of course), such as pink salmon, coho salmon, chum salmon, sockeye salmon and so on, will suit this dish of Russian cuisine. In general, such a salad with smoked fish is often called Amur, and the Far East is considered its homeland. In the magazine where I got this recipe, it was said that such a salad is often prepared by Far Eastern housewives for various holidays. Moreover, it is even served in restaurants. I think this is a very good reason to try to cook this salad.
To make our food more tender, we start with pickling onions. Cut it into rings, pour hot water with vinegar, sugar and salt, soak for about 20 minutes, remove from the water, squeeze and let cool. We cut the fish into thin wide plates, and tomatoes into thin slices. Mix onions, fish, tomatoes, add green peas and pour vegetable oil. The salad should stand for a while to soak well. By the way, the recipe gives advice to use fragrant vegetable oil, that is, something that smells like seeds. Although this is for an amateur.