Cut steak with the grain into 2-inch-thick slices. Cut slices diagonally into thin strips. Combine steak and cornstarch through sake in a large bowl; stir to coat. Cover and marinate in refrigerator 20 minutes.
To prepare bean mixture, combine beans through red pepper in a bowl. Set aside.
To prepare sauce, combine soy sauce through cornstarch in a medium bowl, stirring with a whisk. Set aside.
Place green beans in a large saucepan of boiling water; cook 4 minutes. Drain and plunge beans into ice water; drain.
To prepare stir-fry, heat 3 tablespoons vegetable oil in a large nonstick skillet or wok over medium-high heat. Drain beef; discard marinade. Add beef to pan; stir-fry 2 minutes. Remove beef from pan. Wipe pan with paper towels. Heat 2 tablespoons vegetable oil in pan. Stir-fry bean mixture and onion 1 minute. Add bell pepper; stir-fry 1 1/2 minutes. Add green beans and sauce mixture. Bring to a boil; cook 4 minutes or until thick. Stir in beef. Serve with rice.