Mackerel’s oily flesh means it can withstand strong flavours. Roast the fish until the skin becomes crisp and lightly blistered.
1.Heat the oven to 220C/fan 200C/gas 7. Score the mackerel on both sides a few times with a sharp knife. Whisk together ½ tbsp of garam masala, some seasoning and 1 tbsp of oil. Brush this over the mackerel, rubbing it into the score lines and cavity, or over the fillets. Arrange the lemon slices over a foil-lined baking tray and put the fish on top, then leave to marinate for 10 minutes. Season with sea salt.
2.Meanwhile, heat the remaining ½ tbsp of oil in a frying pan over a medium heat and fry the onion for 6-8 minutes or until softened. Stir in the garlic, ginger, cumin and chilli, and fry for a few minutes until fragrant. Tip in the tomatoes, then rinse out the tin with 200ml of water and add this as well. Simmer for 10 minutes until just thickened.
3.Transfer the mackerel to the oven and roast for 10 minutes if you’re using fillets or 15-20 minutes for a whole fish – the flesh should flake away from the bones and the skin will be lightly crisp when the fish is ready.
4.Stir the chickpeas into the tomatoes and simmer for 5 minutes. Stir in the tamarind to taste and the remaining garam masala. Serve the mackerel over the tamarind chickpeas alongside some roti or chapati and yogurt, with coriander sprinkled over.