Place chicken breast in a single layer in the slow cooker.
Add half a cup/ 118 gram water or broth over the chicken.
Cook on high for 3-4 hours or on low for 4-6 hours.
Put the chicken breast in a big bowl or on a cutting board. Shred using two forks.
Dice the water chestnuts.
Mix all sauce ingredients together.
Combine the sauce well with the shredded chicken.
Serve over washed and dried romaine lettuce leaves or butter lettuce.