HEAT dressing in large skillet on medium heat. Add chicken, in batches; cook 2 to 3 minute on each side or until browned on both sides.
PLACE mushrooms, onions, peppers and garlic in slow cooker; top with the chicken. Combine tomatoes, salt and thyme; pour over ingredients in slow cooker. Cover with lid. Cook on LOW for 6 to 8 hours (or on HIGH for 5 hours).
COOK rice as directed on package. Serve chicken mixture over the rice.