How to Make It
Prepare Spicy Pecan Topping: Preheat oven to 350°F. Combine syrup and butter in a medium microwavable bowl; microwave on HIGH until butter melts, about 45 seconds. Stir in pecans, chili powder, smoked paprika, cayenne, and salt. Spread in a single layer on a baking sheet lined with parchment paper. Bake 8 minutes. Stir mixture; bake until toasted, 4 to 6 more minutes. Remove from oven, and increase oven temperature to 450°F. Cool completely on baking sheet, about 30 minutes.
Prepare Roasted Root Vegetables: Line 2 baking sheets with parchment paper. Combine sweet potatoes, golden beets, and carrots in a large bowl. Drizzle with 3 tablespoons of the oil, and sprinkle with 1 teaspoon of the salt and 1/2 teaspoon of the black pepper. Toss well to combine. Spread mixture in a single layer on 1 baking sheet.
Combine red beets and red onion in same large bowl. Drizzle with remaining 2 tablespoons oil, and sprinkle with remaining 3/4 teaspoon salt and 1/2 teaspoon black pepper. Toss well to combine. Spread mixture in a single layer on second baking sheet.
Bake vegetables at 450°F for 20 minutes. Remove baking sheets from oven; stir vegetables. Tuck 4 thyme sprigs into orange vegetables and 2 thyme sprigs into red vegetables. Rotate baking sheets between top and bottom racks. Bake at 450°F until vegetables are tender, 15 to 20 minutes.
Transfer vegetables to a serving bowl; gently toss together. Coarsely chop pecan topping. Sprinkle topping and thyme leaves over vegetables before serving warm or at room temperature.