Take the duck breast and score the fat layer with a sharp knife in a crosshatch pattern without cutting into the meat below. Cut the pre-cooked beets into equal portions or cubes. Make the dressing by whisking the honey, balsamic vinegar and walnut oil together in a large bowl.
Place the duck breast skin-side down in a cold, dry frying pan and set it over medium-high heat. Cook the meat for about eight minutes so the fat gradually renders and the skin becomes crispy. Then flip the duck breast over and cook the meat side for another three to four minutes.
Remove the meat from the pan and let it rest for five minutes on a cutting board. Meanwhile, add the sliced beets, mâche and walnuts to the bowl with the prepared dressing and gently fold together until everything is well mixed.
Divide the dressed salad over a large plate. Slice the rested duck breast with a sharp knife into neat slices and arrange them on top of the salad. Season the dish finally with freshly ground pepper and sea salt.