Heat oven to 425°F; oil a rimmed sheet. Soak breadcrumbs in milk 3 minutes. Gently mix with turkey, egg, carrot, meatball salt, garlic powder, and pepper. Form 24 meatballs; bake 16 to 20 minutes until 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; cook on HIGH 90 minutes. Fold in drained pineapple and green pepper. Whisk cornstarch with slurry water; stir into sauce.
Cover; cook on HIGH 30 to 40 minutes more until pepper is tender-crisp, 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, then rest off heat 10 minutes.
Divide rice among 6 bowls; top each with 4 meatballs, pineapple, pepper, and sauce. Serve promptly.