Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper.
Drain the extra firm tofu and press it between paper towels to remove excess moisture, then cut into 1-inch cubes.
Slice the purple cabbage into 1-inch thick ribbons and rinse the canned chickpeas, patting them dry with a towel.
Place the tofu cubes, shredded cabbage, and chickpeas onto the prepared baking sheet.
Drizzle with olive oil and sprinkle with sea salt, black pepper, garlic powder, and smoked paprika, tossing everything until evenly coated.
Spread the ingredients in a single layer and roast for 25 to 30 minutes, tossing halfway through, until the cabbage is tender-crisp and the tofu is lightly browned.
While roasting, prepare the dressing by whisking together the tahini, lemon juice, water, and nutritional yeast in a small bowl until smooth and creamy.
Transfer the roasted vegetables and tofu to a serving bowl, drizzle with the lemon-tahini dressing, and garnish with hemp seeds.