Heat oil in a large pan, add in mustard seeds and cook until they start to pop. Add in cumin seeds and cook until golden/fragrant, Then add in onions, and curry leaves, and cook until onions become slightly golden. Mix in garlic and ginger and cook for a few seconds. Then add in the cubed butternut squash. Cover and cook for 10 minutes. Stirring often.
Add kashmiri chili powder, coriander-cumin powder, turmeric powder, cinnamon powder, salt, tomato puree and tinned tomatoes. Give everything a good mix. Cover and cook for 10 more minutes. Stirring often. Add the chickpeas, cover and cook for 5 minutes. Pour in the water, bring to a boil and cook for 2-5 minutes. If you want more gravy, add some more water! Mash a few of the butternut squash cubes to make the gravy of this curry thicker. Mix in the lemon juice, sugar, and coriander. Enjoy!