Preheat the oven to 425°F (220°C).
Season the chicken breasts with salt and black pepper.
In a bowl or jar, mix olive oil, Dijon mustard, maple syrup, balsamic vinegar, garlic, and rosemary until well combined.
Place chicken and sweet potatoes in a large bowl. Pour one-third of the marinade over them and toss to coat evenly.
Spread the chicken and sweet potatoes on a sheet pan and bake for 10 minutes.
Toss Brussels sprouts with another third of the marinade.
Remove the pan, add Brussels sprouts, and return to the oven. Bake for 15–20 minutes until vegetables are tender and slightly crispy, and chicken is cooked through.
Drizzle the remaining marinade over everything before serving.
This sheet pan maple dijon chicken is best served warm straight from the oven.