Preheat the oven to 425 degrees F.
Cut the cauliflower lengthwise into 3/4-inch slices.
In a large bowl, whisk together the olive oil, cumin, smoked paprika, onion powder, garlic powder, salt and pepper. Toss the cauliflower and chickpeas into the mixture. (You can use your hands to do this.)
Arrange the cauliflower in a single layer on a sheet pan. Put the chickpeas in the spaces in between the cauliflower. Roast for 25-30 minutes, flipping just over halfway through cooking, until the cauliflower is browned at the edges and the chickpeas are crispy.
For the herby tahini, puree the garlic, tahini, parsley and cilantro, scallions, lemon juice, salt and water in a food processor until combined and smooth. You want it to have a thick, but slowly pourable/spoonable consistency. Add a little more water as needed.
Drizzle the roasted cauliflower and chickpeas with herby tahini. Sprinkle with chopped parsley and cilantro.