Finely chop the onion. Smash, peel and chop garlic. Roughly chop whole Kashmiri chillies.
Put a frying pan on medium high heat. Add mustard oil/any cooking oil to it. Once the oil is warm, add all the seeds to it – fennel, cumin and nigella. Let these bloom and splutter before adding chopped garlic, onion and chillies. Sauté until the onions start browning. Once onions are done add dry spices – chili powder, turmeric and coriander powder. Stir and cook for a minute and lower the heat. If the pan is too dry, add a splash of water to prevent spices from burning.
Squeeze out water from salted melon peels and add them to the pan. Cook on medium high heat stirring intermittently until all the moisture has been cooked off and the peels are a deep dark green.
Once the peels have cooked, add amchoor and jaggery. Turn off the heat and mix well. Jaggery will caramelize if left on the heat. Stir well until everything is combined and remove to a bowl. Allow this mixture to cool before the next step. Retain the frying pan as is, do not wash it.
If the stuffing doesn’t seem enough, add bean for bulk and more flavor. Mix it well until no lumps remain and continue to roast on low heat till you smell its nutty aroma. Besan will also cook some more in the final step with the karele.