Cook bacon in large skillet over medium-low heat 15 minutes or until crispy. Using a slotted spoon, remove bacon, reserving drippings in skillet. Drain and set aside.
Cut onion in half. Slice halves into 1⁄4-inch slices. Cook in hot drippings over medium-low heat for about 12 minutes, stirring often, or until lightly browned.
While onion cooks, remove outer leaves and stems from Brussels sprouts, and cut in half lengthwise; then cut into 1⁄4-inch slices.
Toss together Brussels sprouts, onion, and desired amount of dressing. Sprinkle with bacon before serving. Serve immediately.