Preheat the oven to 375°F, and line a baking sheet with parchment paper.
Toss the sweet potato and garlic with extra virgin olive oil, 1 ½ tsp salt and ½ tsp pepper, then spread evenly across the parchment-lined baking sheet. Roast in the oven for 15 minutes, toss and return to the oven until the potatoes are soft and golden brown. Approximately another 20 minutes.
Place the chickpeas, lemon juice, tahini, cumin, ¼ tsp pepper and 1 tsp salt into a food processor bowl. Add the roasted sweet potato with the garlic. Purée very well. Once the mix is smooth and just before stopping, drizzle in the olive oil. If the mixture is too thick, gradually add the reserved canned chickpea liquid to loosen.
Adjust the seasoning with salt and lemon juice.
If the ingredients don’t fit in your processor bowl, process in two batches and mix together.