Preheat the oven to 200°C/400°F/gas 6. Peel and halve the onions. Tear up the peppers into big chunks, discarding the seeds and stalks. Place it all in a 35cm x 25cm roasting tray with the chicken, Cajun seasoning and whole unpeeled garlic cloves. Drizzle with 1 tablespoon each of olive oil and red wine vinegar, season with black pepper and toss well, turning the chicken skin side up. Roast for 40 minutes.
Boil the kettle. Remove the tray from the oven and mash the soft garlic cloves into the tray juices, discarding the skins. Around the chicken, pour in 1 mug of rice and 2 mugs of boiling kettle water (600ml). Carefully cover with tin foil and return to the oven for 20 minutes, or until the rice is fluffy and the chicken pulls easily away from the bone.
Season to perfection, then serve with dollops of yoghurt, a pinch of black pepper, and a drizzle of extra virgin olive oil, if you like.