Preheat the oven to 400ºF / 200ºC degrees.
Heat a skillet over medium heat and cook the bacon until the fat has rendered and it is crispy.
Remove the bacon to a plate lined with kitchen paper.
Add the brussels sprouts and onion wedges to the skillet, season with salt and thyme, and toss well to coat in the bacon fat.
Lay the sprouts and onion wedges onto a large baking sheet. Roast in the oven for 30 minutes until tender and golden.
Serve in a large bowl, drizzle with vinegar, and top with crispy bacon pieces.