Preheat grill to medium-high; grease grate well. Grill watermelon wedges, turning once, for 3 to 5 minutes or until grill-marked on both sides. Cut each watermelon wedge into 4 smaller wedges.
Top each cracker with watermelon wedge and sprinkle with feta. Drizzle with balsamic reduction. Garnish with fresh mint.
Tip: Add finely chopped Kalamata olives for a tangy addition.