Place the bacon bits into a bowl. Add the olive oil, and season with salt and pepper. Toss them together until they are well combined.
In a large bowl, toss the Brussels sprouts with the olive oil, salt, pepper, and onion. Then add the bacon mixture to the bowl.
Spread the Brussels sprouts out onto a sheet pan. Bake for 30 minutes or until the sprouts have shrunken and turned a light brown color.
Remove the sheet pan from the oven and sprinkle the Parmesan cheese over the top. Return the pan to the oven and bake for another 5-10 minutes, or until the sprouts are fully cooked and slightly crisped around the edges.