Bake walnuts in a shallow pan at 350°, stirring occasionally, 5 to 10 minutes or until toasted; set aside.
Combine oil and next 5 ingredients; cover and chill.
Cut green beans into thirds, and arrange in a steamer basket over boiling water. Cover and steam 15 minutes or until green beans are crisp-tender. Immediately plunge green beans into cold water to stop cooking process; drain and pat dry.
Combine walnuts, beans, onion, and cheese in a large bowl; toss well. Cover and chill.
Pour oil mixture over bean mixture 1 hour before serving; toss just before serving.