In 4 qt. slow cooker bowl, combine crushed pineapple, soy sauce, brown sugar, rice wine vinegar, garlic, and ginger. Stir well to make sure all ingredients are mixed.
Add chicken. Cook until chicken is tender (High - 4-5 hours : Low - 6-8 hours).Stir about 2-3 times during cooking and push chicken down so it's immersed in the sauce.
Optional: to thicken the sauce (do this about 30 minutes on low, or 5 minutes on high before chicken is finished cooking). Make the corn starch slurry: mix cornstarch and cold water in small bowl. Stir the mixture so that all the cornstarch is completely dissolved, leaving no lumps.
Quickly stir in the cornstarch slurry into the crock pot teriyaki mixture and combine well so that the cornstarch doesn't thicken and become lumpy.Serve over rice or pasta.