Slow Cooker Asian Chicken Lettuce Wraps

lbs ground chicken ((not ground chicken breast))

garlic (, minced)

red bell pepper (, cored and finely chopped)

finely chopped yellow onion

hoisin sauce

soy sauce

Salt and freshly ground black pepper

sliced water chestnuts, drained and rinsed

cooked white or brown rice

green onions (, sliced)

rice vinegar and 1 1/2 tsp sesame oil ((optional))

heads iceberg lettuce