Preheat the oven to 190°C (170°C fan)/gas mark 5. Sprinkle 1 tablespoon plain flour inside a large oven roasting bag, shake to coat and set aside.
In a large bowl, combine the quartered red potatoes, carrot pieces and onion wedges. Drizzle with 1 tablespoon olive oil, season with ½ teaspoon salt, ¼ teaspoon ground black pepper, ½ teaspoon garlic powder and ¼ teaspoon onion powder, then toss to coat.
Pat the chicken dry with kitchen paper. In a small bowl, mix the remaining 1 tablespoon olive oil with ½ teaspoon salt, ¼ teaspoon ground black pepper, ½ teaspoon garlic powder, ¼ teaspoon onion powder, ½ teaspoon dried thyme and ½ teaspoon paprika. Rub this mixture all over the chicken.
Place the seasoned chicken into the prepared bag and arrange the vegetables around it so they’re evenly distributed.
Seal the bag with the tie provided, leaving some space for steam. Cut 4–6 small slits in the top of the bag to vent.
Put the bag in a large roasting tin and bake for 1¼–1½ hours, or until the thickest part of the chicken reaches 75°C and the vegetables are tender.
Remove from the oven and leave the chicken and vegetables to rest in the bag for 10–15 minutes. Carefully open the bag, transfer everything to a serving platter and discard the bag.