Preheat the oven to 400˚F.
Pour the oil into a roasting pan, or ovenproof dish, and put in the oven for about 5 to 8 minutes to heat it up.
Remove pan from oven and add the cauliflower florets, cubed potatoes, and onions to the pan, stirring to coat them with the hot oil.
Season veggies with salt and pepper and return to the oven for 15 minutes, or until beginning to brown.
While the vegetables are roasting, stir together the hot vegetable broth, curry paste, chopped chilli, saffron, and ground mustard.
Remove the pan from the oven and stir in the rice and green beans with the rest of the vegetables; then, pour over the vegetable broth mixture. Stir well to combine.
Lower the oven to 375˚F.
Cover the pan tightly with foil and bake for 30 to 35 minutes, or until the rice is tender and the liquid has been absorbed.
Stir in the lemon juice. Taste for salt and pepper and adjust accordingly.
Top with cilantro and cashew nuts.
Serve with naan and a bowl of raita.