Season the washed Hilsa head with salt and a pinch of turmeric powder. Now fry it in mustard oil till crisp and thoroughly cooked. Take it out in a plate and break into 3 to 4 pieces.
Chop the Malabar spinach roughly. Slice thick stalks into two to help them cook evenly. Set aside.
Heat 2 tablespoons of oil in a wok/kadhai. Fry the diced pumpkins, diced potatoes, diced ridge gourd and diced eggplant separately till golden brown. You do not need to fry them completely. Set them aside.
Add the remaining oil in the same pan. Temper it with nigella seeds and green chili. Let them sizzle.
Now add the chopped spinach and stir fry on high heat. Add half teaspoon of turmeric powder, sugar and salt to taste. Stir thoroughly.
Now add the fried vegetables and mix well. Reduce the heat and cook covered.
You may not need to add water as the spinach itself will leave a lot of water and get cooked in it.
Once all the vegies are three-fourth done, add the pieces of fried Hilsa head. Stir thoroughly to mix well on high heat till all the water evaporates completely and it starts to stick at the bottom of the pan.
The consistency of the final product will be kind of mushy with all the vegetables mashed and mixed with each other.
Serve hot with plain white rice!
Recipe by Flavor Quotient at http://www.flavorquotient.com/2014/09/ilish-macher-matha-diye-pui-shaak-bengali-hilsa-recipe/