Make the Masala: Dry roast peanuts, sesame seeds and cashews separately until golden and nicely roasted. Saute onions in 1tsp oil until lightly browned around the edges. Then grind to a smooth paste adding little water. This masala can be made 2 days ahead and refrigerated until ready to use.
Make the Curry: Heat 3tbsp oil in a pan; saute the veggies (from potato to green chilies on the ingredient list) on medium-high flame either separately or all together for 5-7 minutes, stirring occasionally until they start to change color. This step is only to crisp up the veggies and not completely cook them. Alternately you can deep fry them.
In a large pan, heat 2tbsp oil and add the nigella seeds. Once the seeds start to smell fragrant, add the ground paste, turmeric and cook on medium-low flame, stirring frequently until oil starts to leave the sides, about 8 minutes.
Next add the ground coriander and red chili powder. Cook for a minute.
Next add the sauteed veggies and salt. Add enough water to make the gravy of desired consistency. Bring the mixture to a boil , lower the heat and cook covered until the veggies are tender, about 12-15 minutes.
Add the tamarind paste and cook for another 5-6 minutes.
Garnish with chopped cilantro and serve warm with rice or roti.