Bring two large saucepans of salted water to the boil over a high heat. Add the carrots and potatoes to the first saucepan and cook for 7 to 8 minutes until edible but still a bit hard and not at all mushy. Add the peas in for the final minute. Drain.
Add the rice to the second saucepan and cook for the recommended cooking time depending on the rice you are using, until tender and fluffy. Drain if necessary.
Meanwhile, heat a few tablespoons of olive oil in a large frying pan or wok, over medium heat. Once the oil is hot, add the onions to the frying pan and fry until onions are golden.
Add the chopped tomatoes to the onions and add a teaspoon of sugar to take away the bitterness of tinned chopped tomatoes. Mix in the vegetables and peas and increase the heat to high. Cook for 6 to 7 minutes stirringly constantly.
Season the curry sauce with turmeric, cumin, mustard seeds, if using, and salt. Reduce the heat to medium and simmer for a further 6 minutes.
Stir in your coconut milk. We like our curries quite coco-nutty, so we use the whole tin, but you can use coconut milk to taste. Serve over the rice.