Heat the oil in a large, heavy-bottomed pot. Add the onions and a pinch of salt. Cook the onions for 7 minutes, or until they're very tender and browning lightly. Add a few tablespoons of water as needed to prevent sticking. Add the garlic and ginger. Cook for 2 minutes, or until the garlic is very fragrant. Add the curry, turmeric, garam masala, salt, and black pepper. Give everything a good stir.
Add the squash and 2 cups of the vegetable broth. Bring the mixture to a boil. Reduce to a simmer. Simmer for 15 minutes, or until the squash is tender. Turn off the heat. Use an immersion blender to blend the soup about halfway, so that there are still chunks of butternut squash, but some of the squash has been turned into a thick puree. Alternately, you can transfer half of the mixture to a standing blender, blend, and return it to the pot.
Stir in the chickpeas, raisins, lime juice, and an additional 1/2 cup broth (or enough to create a thick but easy-to-stir stew). Bring the curry to a gentle simmer again. If you're adding greens, stir them in now and allow them to wilt completely, about 5 minutes. Taste the stew and adjust salt, pepper, and lime juice to taste. Serve with cooked grains.