Onions cut into thin half-rings. Marinate in mixture of soy sauce, vinegar and sugar for 10 minutes.

Cut the tomatoes into slices, add the pickled onion, mix well. In the marinade from the onions, add the vegetable oil (I added oil from the mussels), and pepper - it will be the salad dressing.

On a dish place the tomatoes, onion, mussels, garnish with greens and pour dressing.