Cook green beans in large saucepan of boiling salted water until just tender, about 5 minutes. Using slotted spoon, transfer beans to plate. Add orzo to same boiling water. Cook until tender, stirring occasionally; drain.
Blend dill, oil, vinegar, and lemon juice in mini processor until almost smooth. Season dressing with salt and pepper.
Cut beans crosswise into 1/2-inch pieces. Place in large bowl. Add orzo, cucumber, and fennel; mix in dressing. Season salad to taste with salt and pepper.
