Preheat the oven to 425 F.
Cut the sweet potatoes in half lengthwise. Rub the cut side with olive oil and season with salt and pepper then place cut-side down on a baking sheet. Roast for 10-15 minutes before adding the chickpeas.
Once the sweet potatoes are in the oven, add the sliced red onion, chickpeas, all of the spices and 1 tbsp of oil to a second baking sheet and mix until the chickpeas and onion are well-coated in oil and spices. Add to the oven with the sweet potatoes. Roast for 10-15 minutes before adding the broccoli.
Once the chickpeas are in the oven, add the broccoli florets to a third pan with remaining 2 tbsp oil. Season with salt and pepper and mix well to ensure the broccoli is all coated in oil. Add to the oven with the sweet potatoes and chickpeas, moving the sweet potatoes to a lower rack if needed or removing from the oven if they're done. Roast for 10-15 minutes until tender and browned around the edges.
Add all of the tahini sauce ingredients to a bowl or sealable container and mix or shake until fully combined and smooth. Start with 2 tbsp of water then slowly add more to reach your desired consistency.
Once the broccoli is done, remove everything from the oven.
Place two halves of a sweet potato on a plate and fluff the sweet potato flesh with a fork. Top with the chickpeas and onion and broccoli. Drizzle with tahini sauce.