Preheat oven to 350F. 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.