Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Peel the sweet potato and cut it into 1-inch thick wedges or cubes.
Clean the cremini mushrooms with a damp cloth and slice them into halves or quarters depending on size.
Mince the garlic clove finely.
In a large bowl, toss the sweet potato wedges, mushrooms, and minced garlic with 0.5 tablespoon of olive oil, the dried rosemary, and half of the sea salt.
Spread the vegetables in a single layer on one side of the prepared baking sheet.
Rub the chicken breast with the remaining 0.5 tablespoon of olive oil and season both sides with the remaining sea salt and the black pepper.
Place the chicken on the other side of the baking sheet.
Roast in the center of the oven for 20 to 25 minutes, or until the chicken reaches an internal temperature of 165°F and the sweet potatoes are fork-tender.
Let the chicken rest for 5 minutes before slicing and serving alongside the roasted vegetables.