Preheat the oven to 475°F and adjust the oven rack to the middle position. Line a baking sheet with foil.

Remove the outer green leaves from the cauliflower heads and trim the stems (keeping enough stem to leave the cauliflower heads intact).

With a large knife, cut into the center of one of the cauliflower heads to make two equal halves. Then cut a 1½-inch thick "steak" from each half. (If the cauliflower head is large, you might be able to get another steak from each cut side, but usually 2 thick steaks come from one cauliflower head.) Repeat this process with remaining cauliflower head to make 4 cauliflower steaks in total. (Save any leftover cauliflower florets for another use.)

In a small bowl, whisk together the sweet paprika, cumin, salt, garlic powder, smoked paprika, and pepper.

Place the cauliflower steaks on the prepared baking sheet and divide half of the spiced mixture among the four steaks. Drizzle with half the olive oil and massage the steaks to incorporate the spices into the nooks and crannies. Flip each steak and sprinkle with the remaining spice mixture and drizzle with remaining olive oil. Massage again to incorporate the spices into the steaks.

Tightly cover the baking sheet with foil to enclose and bake for 5 minutes. Remove the foil and place back in the oven to roast until golden and crispy, about 10 minutes. Remove from the oven, gently flip the cauliflower steaks with a spatula, and place back in the oven to roast the other side until golden, crispy, and lightly charred, 7-10 minutes.

While the cauliflower steaks roast, prepare the toppings: In a small mixing bowl, combine the chickpeas, paprika, cumin, and salt. Mix to combine.

Transfer the cauliflower steaks to a serving plate and sprinkle with the seasoned chickpeas, drizzle with the tahini, and sprinkle with the parsley.