In a large pot, heat the oil or ghee and add the leek, ginger, and serrano (if using). Sauté until the leeks soften and start to brown slightly.
Add fennel seeds, coriander, cumin, and turmeric, and saute for 1-2 minutes until they become very fragrant. If they are sticking badly and look like they may burn, add a small splash of water.
Add squash, tomatoes, water, and 1 teaspoon sea salt. Bring to a boil, then reduce heat and simmer until the squash is tender when pierced with a fork.
Taste and add more salt, as needed. Serve over cooked quinoa or chickpeas.