Carefully chop or break the cauliflower from the main stem taking care to preserve the natural floret shapes where possible then boil in salted water for 3 minutes. Cool immediately and drain.
In a bowl large enough for the cauliflower but small enough to fit in your fridge mix together the tandoori spice mix, lemon zest, lemon juice, garlic, tomato puree and yoghurt.
Toss the cooked cauliflower in the marinade coating thoroughly. Cover and leave refrigerated overnight.
Heat the oven to 250 Celsius/480 Farenheit
Remove the marinated cauliflower from the fridge and spread in a single layer on a large roasting tray.
Cook at the top of the oven for 20 - 30 mins until lightly charred and baked to your liking.
Turn the cauliflower pieces over halfway through cooking at about the 15 minute mark.
Whilst the cauliflower bakes heat a large pan on medium heat and once hot add the oil and swirl to coat the pan. Carefully add the onions and cook on medium heat for 15 minutes until starting to caramelise.
Add the chilli, garlic, ginger, lemon zest, stock cube, garam masala, turmeric, coriander seeds and stir thoroughly.
After 5 minutes add the mushrooms and lemon juice.
After a further 5 minutes add the rice and peas. Stir constantly to fully coat the rice with the spice mix.
Heat for 5-10 minutes to ensure the rice is fully heated through. Add a splash of boiling water to prevent sticking if necessary.
Serve the Tandoori Cauliflower and Lemon and Mushroom Rice with a Cucumber and Tomato Raita and chappati or pitta bread.