Prepare a 1-litre pickling jar by washing the jar and lid, removing the rubber seal. Place in the oven and heat at 100ºC/gas ¼ for about 30 minutes. Immerse the rubber seal in a pan of boiling water and simmer for about 10 minutes before turning off the heat and allowing to cool.
Peel and finely slice the onions, then peel and finely grate the garlic and ginger. Heat the oil in a saucepan big enough to hold all the ingredients. When smoking hot, add the mustard and fenugreek seeds – they should start to pop right away. Stir in the onion, garlic and ginger, turn the heat down and cook slowly, stirring, till the mixture is dark brown and smells fantastic.
Deseed and roughly chop the pumpkin, and halve and deseed the chillies. Add the remaining spices, stir-fry for a minute or so, then add the tomatoes. Bring to the boil and simmer gently for a few minutes. Grate in the lime zest. Squeeze the lime juice into a measuring jug and top up to 500ml with cider vinegar. Pour into the pan, add the chilli and pumpkin, and bring back to the boil.
Pat the seals for the jars dry with kitchen paper, fit them back onto the lids and have the jars standing by. When the pumpkin is just cooked, lift it out with a slotted spoon into a clean mixing bowl and set aside. Add salt and sugar to the pan, and continue cooking till the liquid is thick. Fold the pumpkin back into the mix, making sure it’s nice and hot before turning the heat off.
Spoon the pumpkin pickle into sterilised jars while everything’s still hot. Wipe the rims of the jars and seal them. Leave to cool, and it will be ready to eat in a few weeks’ time.