Heat the oven to 190°C (Gas Mark 5 / 375°F).
Peel the red onion, and cut it into 1cm wedges. Add it to a large baking dish, along with the cauliflower and potato chunks. Toss the vegetables in a little oil, and season with salt and pepper.
Roast for about 30 minutes, until the potatoes are fairly soft.
While the vegetables are roasting, add the curry paste to the hot vegetable stock, and mix well until fully combined.
When the vegetables are ready, add the green beans, rice, chickpeas and stock to the baking dish, and mix thoroughly. Cover with foil, and return to the oven for about an hour, stirring every fifteen or twenty minutes, until the rice has absorbed the liquid, and the rice and potatoes are totally soft. If the liquid has been absorbed before the rice and potatoes are soft, just add a dash more liquid and return to the oven.
When everything is fully cooked, stir again, and serve with the lemon juice and fresh coriander.