Heat the oven to 425°F and oil a rimmed sheet. Soak breadcrumbs in milk for 3 minutes, then gently mix with turkey, egg, carrot, meatball salt, garlic powder and pepper. Form 24 meatballs and bake for 16 to 20 minutes until the centers reach 165°F.
Meanwhile, bring pineapple juice, broth, ketchup, vinegar, brown sugar and soy sauce to a simmer in a saucepan. Transfer hot sauce and hot meatballs to a 4-quart slow cooker.
Cover and cook on HIGH for 90 minutes. Fold in drained pineapple and green pepper, then whisk cornstarch with slurry water and stir it into the sauce.
Cover and cook on HIGH for 30 to 40 minutes more until the pepper is tender-crisp, the sauce thickens and meatballs remain at least 165°F.
During the final half hour, bring rice, rice water and rice salt to a boil in a saucepan. Cover, reduce to low for 18 minutes and rest off heat for 10 minutes.
Divide rice among 6 bowls and top each with 4 meatballs, pineapple, pepper and sauce. Serve promptly.