In a large skillet set to medium heat, cook bacon until crisp. Leaving the bacon grease in the pan, transfer bacon to a plate covered with a piece of paper towel.
Add shallots to the pan with the grease and sauté 2-3 minutes, or until tender.
Add butter and Brussels spouts and sauté 2-3 minutes.
Mix in apple, chicken, vinegar, salt, and pepper and cook 2-3 additional minutes to allow flavors to come together.
Crumble bacon and toss in with the rest of the ingredients.