For the Italian sausage salad, first peel the onions, quarter them and cut them into tender strips. Clean arugula, rinse, drain well and chop coarsely. Cut tomatoes into thin strips, drain olives.
Mix vinegar with olive oil and tomato strips, season with salt and pepper.
Cut mortadella into coarse pieces. Remove the rind from the pecorino and cut into fine pieces. Mix the onions, pecorino, mortadella and olives with the tomato dressing. As a final step, fold in the arugula and season the Italian sausage salad with coarse pepper.