Preheat the oven to 190°C, fan 170°C fan, gas mark 5. Rub the by chicken with half of the Cajun spices and put it into a roasting pan. Cover with foil and roast in the oven according to the pack instructions.
Meanwhile, put the halved potatoes and garlic onto a separate baking tray with the olive oil and the remaining Cajun rub. Toss together with your hands to coat the potatoes.
About 15 minutes before the end of the chicken’s cooking time, put the tray with the potatoes and garlic into the oven. At the same time, remove the foil from the chicken.
When the chicken has finished cooking, remove it from the oven and set it aside to rest. Increase the oven temperature to 220°C, fan 200°C fan, gas mark 7.
Add the chopped red and white onions and the peppers to the tray of potatoes. Then cook the vegetables for a further 15 minutes, until golden and tender.
Slice the chicken and serve with the roasted vegetables.
Cook's tip: Save any remaining Cajun rub from the pack and use to sipce up some ordinary chips, potato wedges or grilled meats.