Heat oil in a large wide skillet or kadai over medium heat until shimmering. Add mustard seeds. When they pop, add cumin seeds, curry leaves, and hing. Let the leaves splutter for a few seconds, then add onion and green chili with a pinch of salt. Cook 7 to 9 minutes, stirring often, until the onion is soft and turning golden at the edges.
Add ginger-garlic paste. Stir constantly for 60 to 90 seconds until the raw smell fades and the paste looks slightly toasted.
Reduce heat to medium-low. Add coriander powder, cumin powder, turmeric, and Kashmiri chili. Stir for 20 to 30 seconds until fragrant. If the pan looks dry, splash 1 tablespoon water and stir so the spices do not scorch.
Add chickpeas and pumpkin purée. Stir until the pumpkin coats the chickpeas evenly. Pour in coconut milk and 3/4 cup hot water. Add 1 1/4 teaspoons salt. Bring to a gentle simmer (small bubbles, not a rolling boil), then cook 12 to 15 minutes, stirring a few times, until the gravy looks cohesive and slightly thickened. If it tightens too much, add the remaining water a splash at a time.
Turn off the heat. Stir in garam masala and kasuri methi if using. Crush the methi between your palms before adding so it distributes evenly. Taste salt. Stir in lime juice to taste, then fold in most of the coriander, reserving a little for bowls.