Peel onions and cut them into very thin rings. Peel 3 oranges so that the white skin is completely removed. Use a knife to cut out the flesh between the parting skins.
Squeeze the rest of the orange. Clean, wash, drain and pluck the salad into bite-sized pieces. Cut smoked pork loin into strips. Mix orange juice, vinegar, salt, pepper and sugar. Add oil slowly, stir in.
Arrange the salad on plates and spread the marinade over it.