Trim Brussels sprouts, remove damaged leaves, and slice each in half.
Toss sprouts with olive oil, salt, pepper, garlic powder, and onion powder.
Arrange cut-side up on a baking sheet and roast at 375°F (convection) or 400°F (regular) for 20–30 minutes, until golden and crisp.
Cook bacon in a skillet until crisp, then remove and set aside.
In the bacon fat, sauté onions until soft and lightly browned.
Add garlic and cook briefly until fragrant.
Splash in white wine vinegar to brighten the flavors.
Toss roasted sprouts with bacon, onions, and parsley. Serve hot.