Step 1Cook the beets in boiling water until tender, 25 to 35 minutes. Place in a bowl of ice water. Slip off the skins.
Step 2To make the dressing, whisk together the mustard, vinegar, garlic and salt and pepper to taste. Slowly drizzle in the oil, continuing to whisk.
Step 3Toss the greens in dressing (reserving some dressing for the beets) and divide the greens among 4 serving plates.
Step 4Cut the beets and apples into large (half-inch) dice. In a bowl, combine the beet and apple cubes with the cheese, walnuts, parsley and desired amount of dressing (saving the remaining dressing for another use). Spoon the mixture over the dressed lettuce and serve.