1. Preheat your oven to 200°C/Fan 180°C/Gas 6. Add 2 tbsp of the yogurt to a mixing bowl along with 1 tbsp of the tikka masala spice blend (keep the rest). Add ½ tbsp oil and a pinch of salt and stir to mix. Pull the leaves off the cauliflower (you can keep them for stir-fries), then break the cauliflower into small florets. Chop the stalk into bite-size chunks. Add the cauliflower to the spiced yogurt and stir to coat it. Set aside to marinate for 5 mins.
2. Peel and finely chop the onion. Warm a large pan on a medium heat for 2 mins, then add ½ tbsp oil and the onion. Add a pinch of salt and fry, stirring often, for 6-8 mins till glossy and lightly browned.
3. While the onion fries, line a baking tray with baking paper and spread the cauliflower out on the tray. Slide the tray into the oven and roast for 25-30 mins till the cauliflower is lightly charred.
4. Peel and grate or crush the garlic. Peel and grate or finely chop the ginger. Finely chop the coriander stalks (keep the leaves for later). Stir the garlic, ginger and coriander stalks into the onion with another 1 tbsp tikka masala spice blend. Cook and stir for 1 min.
5. Tip the tin of chopped tomatoes into the pan. Half-fill the tin with around 200ml water and add that to the pan. Stir, pop on a lid and bring to the boil, then turn the heat down and simmer for 10-15 mins, stirring occasionally. The sauce should thicken up as it's cooked, but if it seems too dry or too thick, add a splash more water and turn the heat down again.
6. Fill your kettle and boil it. Rinse the rice under cold water, then tip it into a small pan. Pour in 300ml boiling water and add a pinch of salt. Pop on a lid, bring to the boil, then turn the heat right down. Very gently simmer for 8 mins, till all the water has been absorbed. Take the pan off the heat and let the rice steam in the pan, lid on, for 3-5 mins to finish cooking it.
7. Tip the roast cauliflower into the tikka masala sauce and add the baby leaf spinach. Gently stir to mix in the veg and wilt the spinach. Taste and add a pinch more salt if you think it needs it.
8. Fluff the rice with a fork and divide it between 2 warm plates. Top with the cauliflower tikka masala. Serve with the remaining yogurt, garnished with coriander leaves.