To prepare salsa, combine the first 13 ingredients in a medium bowl; stir well. Cover and chill 1 hour.
To prepare shrimp, place butter, 2 teaspoons juice, 1/4 teaspoon salt, garlic, and shrimp in a large bowl; toss to coat. Thread 4 shrimp onto each of 6 (12-inch) skewers. Place kebabs on a grill rack coated with cooking spray; grill for 3 minutes on each side or until shrimp are done. Serve with salsa and lime wedges. Garnish with mint sprigs, if desired.