Liquidize or whisk the ingredients for the dressing.
Wash and dry the required amount of salad leaves and tear into bite-sized pieces. Season the tomato concassé with salt, freshly ground pepper and sugar. Cut the scallions, both green and white parts, into slices at an angle. Wash the mussels well, put them into a heavy frying pan in a single layer, cover with a folded tea-towel and pl