Preheat the oven to 400°F (200°C).
In a bowl, whisk together the maple syrup, Dijon mustard, olive oil, garlic powder, salt, and pepper.
Place the chicken breasts in a baking dish and pour the marinade over them, ensuring they are well-coated.
Meanwhile, toss the cubed sweet potatoes in olive oil, salt, and a sprinkle of pepper, then spread them on a parchment-lined baking sheet.
Place the baking dish with the chicken in the oven on the center rack, and the sweet potatoes on a lower rack.
Bake the chicken for about 25-30 minutes or until the internal temperature reaches 165°F (75°C).
Roast the sweet potatoes for 25-30 minutes or until tender and caramelized, stirring halfway through.
Once cooked, remove both the chicken and sweet potatoes from the oven and let them rest for 5 minutes.
Serve the chicken sliced with the sweet potatoes on the side, garnished with fresh thyme or rosemary if desired.