Place baking tray in oven and set temperature to 425 F.
Into large bowl, place sweet potato pieces. When oven reaches desired temperature, dress with 1 Tbsp olive oil, nigella seeds, and salt. Toss to coat evenly and pour immediately onto hot baking tray. Roast at 425 F for 20 minutes, stirring once at the 10 minute mark, until tender and slightly browned, but firm.
Meanwhile, in large bowl, whisk together remaining 1 Tbsp olive oil, lemon juice, lemon zest, garlic, tahini, and black pepper. Add chickpeas and carrot and stir to coat evenly. Add cilantro and parsley, stir once more to incorporate, and allow mixture to marinate while sweet potato roasts.
When finished roasting, remove sweet potatoes from oven and allow to cool slightly. Add spinach to chickpea carrot mixture along with 1/2 the sweet potato cubes, and toss gently to avoid breaking them. To serve, arrange salad on large platter and place remaining sweet potato cubes on top. Be sure to scrape all toasted nigella seeds from baking pan.
Enjoy!