Cook: Roughly chop cauliflower and onion. Add to slow cooker along with cashews and broth. Submerge the cauliflower and cashews under the broth as much as possible, then cover and cook until cauliflower is tender (high for 3 to 4 hours, low for 6 to 8).
Blend: When cauliflower is tender, puree the mixture until smooth using either a handheld immersion blender or by carefully transferring to a countertop blender.
Serve: Stir in 1 to 2 cups water, until you reach a thick, soupy consistency (it will differ depending on the size of your cauliflower). Season with salt and optionally top with crispy chickpeas (see below).
Preheat oven to 400 degrees F. Toss chickpeas with oil, spices, and salt. Spread onto a parchment-lined baking sheet and bake for 20 to 25 minutes, or until crispy. Serve warm over soup.