While rice is cooking, in small bowl, combine oyster sauce, water and cornstarch; blend well. Set aside.
Spray large nonstick wok or skillet with nonstick cooking spray. Heat over medium-high heat until hot. Add beef and garlic; cook and stir 2 to 3 minutes or until beef is browned.
Stir in asparagus, water chestnuts, bell pepper and oyster sauce mixture. Reduce heat to medium-low; cover and cook 3 to 5 minutes or until vegetables are crisp-tender. Serve over rice.