Clean, wash and drain the field lettuce. Core the apple with the skin and cut into fine wedges. Peel the onion, cut in half and cut into strips. Roughly chop the walnuts.
For the salad sauce, squeeze the lemon. Mix the juice with the mustard and season with salt and pepper. Withhold the rapeseed oil. Spread the dressing over the field salad. Cut the cheese and smoked pork into fine wedges and arrange on a salad plate with the remaining ingredients.