Put rice in a medium saucepan and add the turmeric, if using. Pour enough boiling water over the rice to come to about 3/4 inch above the rice (roughly 2 3/4 cups water).
Cover with the lid and return to a boil. Then reduce heat to low and cook as long as package instructions direct.
While the rice is cooking, give the chicken a little toss, then trim and finely slice green onions (both green and white bits), peel and grate the ginger, and peel and finely chop the garlic.
Add green onions, ginger and garlic to the chicken along with the cream, tomato purée, toasted spices and mustard powder. At this stage, the sauce may not look its prettiest, but keep stirring it and once it starts looking more like the chicken tikka masala you know, leave it to bubble away on a low to medium heat for a few minutes to cook the chicken through.
Check that the rice is tender, having absorbed all the water. Fluff it up with a fork, season with salt and pepper, add a drizzle of oil if you like, then cover again to keep the rice warm.
Check that the chicken is cooked. Taste the sauce, adding more heat (with paprika) or seasoning, to your taste. If the sauce is too thick, add a little water; if it is too thin, let it bubble away a bit longer to thicken.