In a bowl pour in the pineapple juice and soy sauce plus your 3 tablespoons of cornstarch and mix well add brown sugar and ketchup and continue mixing.Place chicken breast in the crock pot pour mixture over the top, toss in minced garlic, pepper, cilantro and top with pineapple slices. Spoon some of the mixture over the top of the pineapples, cover and set crock pot.Cook on high for 3-4 hours, or low for 7-8 hours. When the chicken has an internal temperature of 165º it's done.