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.
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.
Place rice on each of 6 plates. Top with chicken thighs and sauce.