To make Barbecue Marinade/Sauce: In large bowl, whisk together ketchup, soy sauce, honey, vinegar and mustard until well combined. Cover; set aside. (Yield: 2 quarts)
With sharp knife, score the skin of each duck breast in a diamond pattern. (Do not cut into the flesh.) Season breasts on both sides with salt and pepper. Place in non-reactive container. Pour 1 quart Barbecue Marinade/Sauce over duck breasts; turn to coat. (Reserve remaining Barbecue Marinade/Sauce.) Cover and refrigerate up to 12 hours.
For each serving, to order: Remove 1 duck breast from marinade. Grill breast 9 to 12 minutes or until desired doneness, turning once and basting with additional 1 1/2 tablespoons of the reserved Barbecue Marinade/Sauce during the last few minutes of grilling. Remove from grill; let stand 5 minutes. Slice breast on the bias. Toss 1 cup (1 ounce) greens with 1 tablespoon vinaigrette. Plate duck breast slices over salad. Drizzle 1 tablespoon additional reserved Barbecue Marinade/Sauce over breast.
Recipe courtesy of Chef Christian Delouvrier, Lespinasse, New York.