Using a paring knife, trim off the base of each brussels sprout, then cut lengthwise into quarters. Place the sprout quarters in a bowl, add the oil and
While the sprouts are cooking, in a nonstick frying pan, cook the bacon over medium heat, stirring as needed to prevent burning, until almost crisp, about 7 minutes. Stir in the walnuts and then the maple syrup and continue to sauté until the mixture is bubbly, about 2 minutes. Set the pan aside with the ingredients in it.
When the brussels sprouts are ready, transfer them to a serving bowl. Return the frying pan to medium-high heat, and when mixture starts to sizzle, stir in the vinegar and let cook until bubbly, about 10 seconds. Pour the bacon mixture over the sprouts, carefully scraping every bit from the pan into the bowl. Season with lots of pepper, then toss well and serve right away.