Preheat your oven to 425°F (220°C). Line a half baking sheet with foil and spray with nonstick spray. In a small dish, stir together the sweet chili sauce and gluten-free tamari. Set aside.
Trim the ends off the Brussels sprouts, then slice them in half. Discard any outer leaves that fall away. Place the halved sprouts on the prepared baking sheet, drizzle with extra virgin olive oil, and season with garlic powder, salt, and pepper. Toss the sprouts with your fingers to evenly coat them, then spread them out in an even layer, cut side down.
Roast the Brussels sprouts in the preheated oven for 15-17 minutes, or until they are golden brown.
Remove the sprouts from the oven and use a pastry brush to gently brush the tops with the sweet chili sauce mixture. Return the sprouts to the oven and roast for an additional 5-7 minutes, or until the glaze is hot and bubbly. Be sure to watch them carefully to avoid burning.
If desired, sprinkle with chopped peanuts before serving.