In a blender or food processor, sprinkle gelatin over buttermilk; let stand for 5 minutes to soften.
Heat orange juice to boiling, then add to blender with honey.
Cover container and whirl on low speed until well blended.
Pour mixture into a bowl, cover, and chill until thick and syrupy (about 1 hour).
Cut rind off melon, discard seeds, and cut fruit into small pieces; you should have about 1 1/2 cups.
Peel, pit, and slice peaches.
Stir cantaloupe, peaches, strawberries, and walnuts into gelatin mixture; pour into a 1-quart ring mold.
Cover and chill until firm (at least 4 hours or overnight).
To unmold, dip in warm (not hot) water for about 10 seconds; run a knife tip around edge to loosen.
Place a serving plate over mold; invert both and shake gently to loosen.
Garnish with whole strawberries, if desired.