Preheat the oven to 425℉.
Season the chicken breasts well with salt and pepper.
Add the olive oil, dijon mustard, maple syrup, balsamic vinegar, garlic, rosemary, salt and pepper to a glass jar. Secure the lid and give everything a good shake.
Place the sweet potatoes and chicken in a large bowl. Pour about one third of the maple dijon mixture over the chicken and sweet potatoes, and give everything a toss to fully coat. Spread the chicken and sweet potatoes out on a large sheet pan. Bake for 10 minutes.
While the chicken and sweet potatoes are in the oven, add the Brussels sprouts to the same bowl. Pour another third of the maple dijon mixture over the sprouts and toss to coat well.
Add the Brussels sprouts to the sheet pan with the chicken and sweet potatoes. Bake for another 15-20 minutes until the Brussels are browned and crispy.
Drizzle the remaining maple dijon mixture over the chicken, sweet potatoes, and Brussels Sprouts before serving.
