Pour small amount of a 12 ounce can V-8 juice into medium bowl. Add one envelope Knox unflavored gelatin to it. Stir gently. In small pot, bring rest of V-8 to a boil and pour over the gelatin mixture. Stir to melt the gelatin. Squeeze one lemon into the V-8 and pour into molds that have been filled with chopped artichoke hearts and/or avocado slices. Chill overnight. These may be made in individual molds, a ring mold or an 8"x8" pan. Serves 4 to 6.