Combine chicken, olive oil, lime juice, salt, pepper, and minced garlic. Toss. Wrap plum wedges with prosciutto. Thread chicken, basil leaves, red onion, and plums alternately onto skewers. Place skewers on a grill rack coated with cooking spray. Grill 8 minutes or until chicken is done, turning skewers occasionally for an even char. Sprinkle with 2 tablespoons fresh basil.
Note: If using wooden skewers, soak them in water for 20 minutes before grilling.