Season chicken pieces with salt and pepper. In a small bowl, mix together Cajun seasoning and garlic powder. Sprinkle seasoning over chicken pieces and then place chicken into the slow cooker.
In a bowl, whisk together the brown sugar, pineapple juice and soy sauce; pour over and around chicken. Cover and cook on low for about 5 hours. Using a tong, transfer chicken from the slow cooker to a platter and loosely tent with aluminum foil.
Prepare the sauce: Transfer remaining mixture from the crockpot to a saucepan and place on the stovetop. Turn the heat to medium high and let the mixture comes to a boil. Whisk together the water and cornstarch until there are no lumps. Slowly stir into the boiling sauce until fully incorporated and continue boiling for about 3 to 4 minutes or until mixture thickens.
Brush the sauce over each chicken thigh and serve the remaining sauce at the table.