
Heat the oil in a frying pan or saucepan, then add the onions, cumin seeds, and a pinch of salt. Cook slowly on low-medium heat for 15 minutes, stirring occasionally until the onion turns brown on the edges.
Add the garlic, ginger, cumin powder (if not using seeds), and a modest amount of salt. Fry for a minute, stirring frequently.
Add the curry powder, and optionally the chilli powder and fenugreek. Stir frequently for another minute.
Add the fresh chillies and tomato purée with a mug of water or stock (about 300ml). If using passata or tinned tomatoes, use half a mug (150ml) of water/stock instead. Turn the heat up to medium-high, mix well, then cook for 20 minutes, stirring occasionally.
Squeeze in the lemon juice, add the protein and vegetables, mix, and let warm through for a couple of minutes.
Add more water or stock to thin the sauce if desired, then taste and add more salt if needed. Serve topped with fresh coriander and a sprinkle of garam masala if you have some.