Prepare and roast the sweet potato by preheating your oven to 400°F (200°C). Wash and dry the purple sweet potato, prick it all over with a fork, then wrap it in aluminum foil. Place it on a baking sheet and roast for 25-30 minutes until completely tender when pierced with a knife.
Let the sweet potato cool until comfortable to handle, about 10 minutes. Peel away the skin and roughly chop the flesh.
Add the chickpeas, tahini, and garlic to your food processor and pulse several times to begin breaking down the chickpeas.
Add the roasted purple sweet potato, lemon juice, olive oil, cumin, and salt to the food processor. Process for about 1-2 minutes until the mixture is relatively smooth.
Check the consistency and with the processor running, gradually add cold water through the feed tube one tablespoon at a time until you reach your desired creaminess. Process for another 1-2 minutes until completely smooth.
Taste and adjust seasoning as needed, adding more salt or lemon juice to balance the sweetness of the potato.
Transfer to a serving bowl and create a shallow well in the center with the back of a spoon. Drizzle with additional olive oil and add your chosen garnishes.
Allow the hummus to rest for at least 30 minutes before serving to let the flavors meld together.