Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper for easy cleanup.
Peel the sweet potato and dice it into 1/2-inch cubes, then trim the ends of the Brussels sprouts and slice them in half.
Cut the chicken breast into even 1-inch pieces to ensure they cook at the same rate as the vegetables.
In a large mixing bowl, combine the chicken, sweet potatoes, and Brussels sprouts with the avocado oil, rosemary, garlic powder, salt, and pepper.
Toss everything thoroughly until the ingredients are evenly coated in the oil and spices.
Spread the mixture onto the prepared baking sheet in a single layer, making sure not to crowd the pan so the vegetables can crisp up.
Roast for 20 to 25 minutes, tossing the ingredients halfway through, until the chicken is cooked through and the vegetables are tender with charred edges.