In a large skillet over medium-high heat, cook the chopped bacon. Once the bacon is cooked but not yet crispy, add in the chopped onions. Continue cooking, for another 3 minutes, until the 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.