Cook green beans in boiling salted water to cover, in a large Dutch oven, 10 to 15 minutes or until crisp tender. Drain.
Melt butter in a large skillet over medium-high heat; add onion, and sauté 5 minutes or until tender.
Add sliced zucchini, and sauté 3 to 4 minutes or until tender. Stir in beans, bacon, salt, and pepper, and cook 2 to 3 minutes or until thoroughly heated. Serve immediately.