Preheat oven to 350°F. Remove any torn or discolored outer leaves from the Brussels sprouts. Trim the bases and cut the sprouts in half.
Render the bacon over medium heat in a medium skillet for about 5 minutes. Add onion, cook 2-3 more minutes. Add the Brussels sprouts and cook until slightly browned. Reduce the heat to medium-low and add thyme, salt and pepper.
Roast in the oven for about 15 minutes. Mix gently and serve.