Set your crockpot to high, and add the onions, ginger, garlic, and coriander leaves. Stir to mix, season with salt and ground black pepper, cover, and let it cook a little while you prep your other ingredients.
Add the butternut squash, potatoes, lentils, cayenne, turmeric and garam masala. Add three cups of water or vegetable stock. Stir well, season with salt, cover, and let it cook for two hours. Check once or twice and add another cup of water if needed. The dal will thicken up as it stands, so don't make it too dry.
Turn off the heat and stir in the cashew yogurt. Garnish with spring onions, if using.
Serve hot with roti or rice.