Place the chicken breasts in the bottom of a 6-quart or larger slow cooker.

In a medium bowl, whisk together the crushed pineapple (with juice), ketchup, soy sauce, brown sugar, cider vinegar, ground ginger, and minced garlic until the brown sugar is dissolved.

Pour the prepared sauce evenly over the chicken breasts in the slow cooker.

Cook on LOW for 6 to 8 hours, or on HIGH for 3 to 4 hours, until the chicken is fully cooked and easily shreds with a fork.

Carefully remove the chicken to a cutting board and shred it using two forks. Return the shredded chicken to the slow cooker and stir to coat thoroughly with the sauce.

Optional Thickening Step: If the sauce is too thin, mix the cornstarch and water in a small bowl to create a slurry. Stir the slurry into the sauce in the slow cooker. Cook on HIGH for about 15-20 minutes, stirring occasionally, until the sauce has thickened slightly.

Serve hot over steamed white rice, brown rice, or alongside pineapple slices and a sprinkle of sesame seeds and chopped green onions for garnish.