Place ground chicken and garlic in a skillet and cook until chicken is no longer pink approximately 10 minutes.
Add cooked meat to the slow cooker. If you have a slow cooker that has a stovetop function, you can cook the chicken in the slower cooker.
After the chicken is cooked through, add bell pepper, onion, hoisin sauce, soy sauce, ¼ cup of water, ½ teaspoon salt, and ½ teaspoon pepper and toss mixture.
Cover and cook on low heat for 3 to 4 hours until chicken is tender.
Stir in water chestnuts, cooked rice, green onions, rice vinegar, and sesame oil, and cook until heated through approximately 3 - 5 minutes.
Season with additional salt as desired.
Separate iceberg lettuce leaves and serve with chicken filling and optional toppings.