Preheat your oven to 425°F (220°C). Line a large 18x13-inch rimmed half-sheet baking pan with parchment paper or lightly coat with olive oil.

Pat the chicken thighs completely dry with paper towels on both sides (critical for crispy skin). Rub with 1 tablespoon of olive oil, then season evenly with garlic powder, smoked paprika, dried oregano, 1/2 teaspoon sea salt, and 1/4 teaspoon black pepper.

In a large mixing bowl, combine the cubed sweet potatoes, halved Brussels sprouts, minced garlic, chopped rosemary, thyme, remaining 1 tablespoon olive oil, Dijon mustard, maple syrup, remaining 1/2 teaspoon salt, and 1/4 teaspoon pepper. Toss thoroughly until glossy and coated.

Spread the seasoned vegetables across the baking sheet in a single layer, turning Brussels sprouts cut-side down for maximum browning. Nestle the chicken thighs skin-side up between the vegetables, ensuring chicken and vegetables do not overlap.

Transfer the sheet pan to the middle oven rack. Roast at 425°F for 30 to 35 minutes without flipping the chicken, until the chicken skin is deeply golden, blistered, and crisp (internal temperature reaching 175°F for tender thighs), and the sweet potatoes are fork-tender.

Remove the sheet pan from the oven and let rest for 5 minutes so juices redistribute. Spoon savory pan drippings over the vegetables, garnish with fresh thyme sprigs, and serve warm directly from the pan.