Preheat your oven to 400°F (200°C) and line a large rimmed sheet pan with parchment paper for easy cleanup.
Peel and dice the sweet potato into 1/2-inch cubes, and trim and halve the Brussels sprouts.
Cut the chicken breast into even 1-inch bite-sized pieces to ensure they cook at the same rate as the vegetables.
Place the chicken, sweet potatoes, and Brussels sprouts onto the prepared sheet pan.
Drizzle the extra virgin olive oil over the ingredients, then sprinkle evenly with sea salt, black pepper, garlic powder, and dried rosemary.
Toss everything together with your hands or tongs until well-coated, then spread into a single layer so nothing is crowded.
Roast in the center of the oven for 20 to 25 minutes, tossing halfway through, until the chicken reaches an internal temperature of 165°F and the vegetables are golden and tender.
Remove from the oven and let rest for 2 minutes before serving.