1. Preheat oven to 400°.
2. Place Brussels sprouts and red onion on a baking sheet. Drizzle olive oil over vegetables, and sprinkle with salt and pepper, tossing to coat. Sprinkle bacon over top of vegetables.
3. Bake at 400° for 45 minutes or until Brussels sprouts and onion are golden and tender and bacon is crisp, stirring every 20 minutes.