BLEND dressing, 1/4 cup mint and 4-1/2 tsp. chiles in blender until smooth. Chop remaining mint with knife, set aside.
PEEL, seed and chop 1 cucumber; place in medium bowl. Add berries, onions, remaining chiles and 1/4 cup dressing mixture; mix lightly.
CUT remaining cucumber into very thin slices. Toss with remaining dressing mixture and chopped mint; place on platter. Top with berry mixture. Squeeze lemon wedges over salad just before serving.
