Heat the oven to 425°F (220°C). Toss the sweet potato and chickpeas with the oil, paprika and a good pinch of salt, and spread them on a sheet pan. Roast for 25–30 minutes, stirring once, until the potato is tender and the chickpeas are crisp.
Meanwhile, combine the quinoa, water and a pinch of salt in a saucepan. Bring to a boil, cover, and simmer on low for 15 minutes. Turn off the heat and leave covered for 5 minutes, then fluff with a fork.
For the dressing, whisk the tahini, lemon juice and garlic. It will seize up at first; whisk in cold water a tablespoon at a time until smooth and pourable. Season with salt.
Divide the greens and quinoa among bowls. Top with the roasted sweet potato, chickpeas, cucumber, avocado and seeds, then drizzle with the dressing.