1. Peel and finely chop the onion. Put a mediumsized pan on a medium heat and warm for 1 min, then add 1 tsp each cumin seeds and black mustard seeds. Toast for 1 min till the seeds pop and smell aromatic, then tip them into a bowl.
2. Put the pan back on the heat and turn it down to low. Add 1 tbsp oil and the onion. Season with a pinch of salt and fry for 3 mins, stirring often, till the onion starts to look glossy.
3. While the onion fries, halve the pepper and scoop out the seeds and white membrane. Roughly chop the pepper. Roughly chop the tomatoes. Stir them into the onion and turn the heat up a little. Fry, stirring every so often, for 10 mins till the tomatoes start to collapse.
4. While the veg fry, finely chop the coriander stalks (keep the leaves for later). Stir the stalks into the veg. Add the toasted cumin and black onion seeds to the pan, and stir in 1 tsp each turmeric and garam masala. Drop in the bay leaf. Add 1 tbsp Dijon mustard. Give everything a stir to mix.
5. Pour 300ml boiling water into the pan. Pop on a lid (or use a baking tray if you don’t have a lid) and turn up the heat. Bring to the boil, then turn the heat down a little and simmer for 10 mins to make a curry sauce.
6. While the sauce cooks, rinse the rice under cold water then tip it into a small pan. Add 300ml boiling water and a pinch of salt. Clamp on a lid and bring to the boil, then turn the heat right down and gently simmer for 8 mins. Once the water has been absorbed, take the rice off the heat and let it sit in the pan, lid on, for 5 mins to finish cooking the rice.
7. The curry sauce should be combined and a little thickened. Add the fish pie mix to the sauce and gently stir to mix. Pop the lid back on and gently simmer for 5 mins till the fish is cooked through – it should be opaque, and flake easily when pressed with a fork.
8. Fluff the rice with a fork and divide between 2 warm plates or bowls. Taste the fish curry and add a pinch more salt if you think it needs it. Ladle the curry over the rice and garnish with the coriander leaves to serve.