Preheat oven to 400°F (200°C). Line two large baking sheets with parchment paper. Peel carrots and cut into uniform 2-inch pieces. Trim Brussel sprouts, discard loose leaves, and halve (or quarter larger ones).
In a large bowl, combine prepped carrots and Brussel sprouts. Drizzle with 3-4 tablespoons olive oil. Sprinkle with 1 teaspoon kosher salt, ½ teaspoon black pepper, ½ teaspoon garlic powder, and optional ¼ teaspoon onion powder & ¼ teaspoon red pepper flakes. Toss thoroughly until all vegetables are evenly coated.
Arrange seasoned vegetables in a single layer on the prepared baking sheets, ensuring ample space between pieces. Roast for 20-25 minutes. Remove, flip vegetables, and return to oven for another 15-20 minutes, or until tender-crisp and beautifully caramelized with crispy edges.
Once roasted, remove vegetables from the oven. Drizzle ¼ cup pure maple syrup evenly over both sheets and toss gently to coat every piece. For deeper caramelization, return to the oven for an additional 5-7 minutes, watching closely to prevent burning.
Transfer the glazed carrots and Brussel sprouts to a serving platter. Garnish with optional 1 tablespoon fresh chopped parsley or a drizzle of balsamic glaze for added tang. Serve immediately while hot and crispy.