Place the chicken thighs at the bottom of the slow cooker.
In a mixing bowl, combine the pineapple juice, diced pineapple, soy sauce, brown sugar, minced garlic, and minced ginger. Mix well.
Pour the mixture over the chicken in the slow cooker, ensuring all pieces are well-coated.
Season with salt and pepper to taste.
Cover the slow cooker with its lid and set it to cook on low for about 6 hours or high for 3 hours, until the chicken is tender and cooked through.
When finished, remove the chicken and shred it with two forks.
In a small bowl, mix the cornstarch with water to create a slurry. Stir this mixture into the juices in the slow cooker and turn it to high.
Cook for an additional 15-20 minutes until the sauce thickens.
Return the shredded chicken to the slow cooker, mix well, and serve.