1. Preheat your oven to 400 F (200 C). Line a large rimmed baking sheet with parchment paper.

2. In a large bowl, combine the cubed sweet potatoes and halved Brussels sprouts. Drizzle with 2 tablespoons of olive oil, then sprinkle with half of the salt, pepper, rosemary, and thyme. Toss everything together until the vegetables are evenly coated.

3. In a separate medium bowl, place the boneless, skinless chicken thighs. Drizzle with the remaining 1 tablespoon of olive oil and sprinkle with the remaining salt, pepper, rosemary, thyme, and the garlic powder. Toss to ensure each piece of chicken is well coated with the seasonings.

4. Spread the seasoned sweet potatoes and Brussels sprouts in a single layer on one side of the prepared baking sheet. Arrange the seasoned chicken thighs on the other side of the same baking sheet, making sure not to overcrowd the pan.

5. Place the sheet pan in the preheated oven and roast for 15 minutes.

6. After 15 minutes, carefully remove the sheet pan from the oven. Using tongs, flip the chicken thighs and gently stir the vegetables to ensure even browning. Return the pan to the oven and continue roasting for another 15-20 minutes, or until the chicken is cooked through (internal temperature reaches 165 F / 74 C) and the vegetables are tender and slightly caramelized.

7. Once cooked, remove the sheet pan from the oven. Let the chicken rest for a few minutes before serving.