1. In a large skillet, heat oil; stir-fry vegetables until crisp-tender.
2. Add sausage and pineapple; cook and stir until heated through.
3. In a small bowl, combine water, cornstarch, soy sauce, sugar and reserved pineapple juice.
4. Add to skillet; bring to a boil, stirring constantly until thickened, about 2 minutes.
5. Serve immediately over rice.