Sprinkle chicken with thyme, salt and pepper. In a skillet, brown chicken in oil. Meanwhile, drain pineapple, reserving the juice. Cut pineapple rings in half and set aside. Combine cornstarch and 2 tablespoons juice until smooth; set aside.
Combine mustard, honey, garlic,and remaining pineapple juice; mix well. Add to pan; bring to a boil. Reduce heat; cover and simmer for 15-20 minutes or until chicken juices run clear. Remove chicken and keep warm. Stir cornstarch mixture and add to pan; bring to a boil. Boil and stir for 2 minutes. Return chicken to pan. Top with pineapple; heat through. Serve over rice.