If you have a very big butternut, you will actually be able to put it on a trivet on top of the presoaked chickpeas and cook at the same time. But anything less than 1kg in size will be too soft. 

To cook the chickpeas, drain them and place in the Instant Pot covered by at least 2 inches of cold water. Cook for 13 minutes on Manual High and QPR. (If you have forgotten to presoak them overnight, cook for 20 mins on Manual High and then QPR). 

To cook the butternut separately, place the peeled, deseeded halves (or quarters if it very large) on the trivet and add 250 ml water to the pot. Cook for 10 minutes on Manual High with QPR. Carefully lift out and allow to cool for a couple of minutes before cutting into 1-2 inch sized chunks. 

In the cleaned out Instant Pot, add the oil and set to Sauteé adjusting to more heat. When hot, add the onions and cook until softened and browned (not burnt - you will need to keep stirring them to prevent sticking).

Add the garlic and ginger, cooking for a minute until fragrant then add the dried spices and cook again until fragrant. Stir very well

Add the tomato purée, coconut milk, tamarind and fresh coriander (reserve a little to garnish with). Cook for a minute before carefully stirring in the cooked chickpeas and butternut.

It will be quite liquid at this point but have faith and keep cooking for a couple more minutes - the gravy will evaporate all of a sudden and become much thicker. Add a little vegetable stock or even just water if you like more sauce. Dig in and serve with naan or rice (or both) as liked.