In a large skillet over medium-high heat, cook chopped bacon. Once bacon is cooked but not yet crispy, add in chopped onions. Continue cooking, for another 3 minutes, until onion is golden and translucent.
Add in Brussels sprouts, and toss to combine. Cook for about 8-10 minutes, stirring often until Brussels sprouts have softened. Reduce heat to low, cover and allow them to steam for about a minute.
Season with salt and pepper to taste, sprinkle blue cheese on top, drizzle balsamic vinegar, and toss to combine. Serve immediately.