Place ground chicken and garlic in a large microwave safe bowl. Microwave mixture, stirring occasionally, until chicken is no longer pink, about 5 - 6 minutes. Drain off liquid and pour mixture into a 5 - 7 quart slow cooker.

Add bell pepper, onion, hoisin sauce, soy sauce, 1/2 tsp salt and 1/2 tsp pepper and toss mixture. Cover and cook on low heat 2 - 3 hours until chicken is tender.

Stir in water chestnuts, cooked rice, green onions, rice vinegar, and sesame oil, cook until heated through 3 - 5 minutes. Season with additional salt as desired. Separate iceberg lettuce leaves and serve with chicken filling.