Preheat the oven to 400 degrees F and line a baking sheet with parchment paper for easy cleanup.
In a small bowl, whisk together the maple syrup, Dijon mustard, 1 tablespoon olive oil, and minced garlic until smooth.
Place the chicken breasts on the prepared baking sheet and brush them evenly with the maple Dijon mixture.
In a separate bowl, toss the halved Brussels sprouts with the remaining tablespoon of olive oil, salt, and black pepper.
Arrange the seasoned Brussels sprouts around the chicken on the baking sheet in a single layer.
Bake for 20 to 25 minutes until the chicken reaches an internal temperature of 165 degrees F and the Brussels sprouts are browned and tender.
Remove from the oven and sprinkle with chopped parsley before serving.