HEAT oil in large nonstick skillet on medium-high heat. Add chicken; cook until each piece is evenly browned on both sides, turning once. Transfer chicken to slow cooker sprayed with cooking spray.
SPRINKLE with seasoning mix, garlic powder and cumin. Add onions and peppers; cover with lid. Cook on HIGH 5 hours or until chicken is done (165°F).
TRANSFER chicken to platter. Carefully ladle liquid from slow cooker into 1-qt. glass measuring cup. Add enough boiling water to reserved liquid to measure 1 qt. (4 cups). Return liquid to slow cooker. Add rice; stir. Cover; let stand 5 min. Fluff rice with fork. Serve with chicken.