1. Sprinkle chicken with pepper and salt. Heat a large nonstick skillet over medium-high heat. Add oil to pan; swirl to coat. Add chicken to pan. Cook 2 to 3 minutes on each side or until browned. Transfer chicken to a 4-quart electric slow cooker coated with cooking spray. Stir pineapple juice into drippings, scraping pan to loosen browned bits. Remove from heat; stir in brown sugar and soy sauce. Pour juice mixture over chicken. Cover and cook on LOW for 2 1/2 hours.
2. Transfer chicken to a serving platter with a slotted spoon. Increase heat to HIGH. Combine 3 tablespoons water and cornstarch in a small bowl; add to sauce in slow cooker, stirring with a whisk. Cook 2 minutes or until sauce thickens, stirring constantly with whisk.
3. Place rice on each of 6 plates. Top with chicken thighs and sauce. Sprinkle each serving with green onions.