Heat oven to 425°F. Toss zucchini chunks with 1 tablespoon olive oil and salt on a baking sheet. Spread in a single layer and roast for 20-25 minutes, turning once halfway through, until edges are deeply caramelized and centers are very tender. Let cool slightly.

In a food processor, combine tahini, garlic, lemon juice, cumin, and remaining 1 tablespoon olive oil. Process until thick and lightly whipped, about 30 seconds, scraping down the sides once.

Add the warm roasted zucchini and chickpeas to the processor. Blend until completely smooth, 2-3 minutes, stopping to scrape down the sides as needed. The warmth from the zucchini helps create a silkier texture.

With the processor running, drizzle in ice water one tablespoon at a time until the hummus reaches a light, spreadable consistency. It should ribbon off a spoon rather than hold stiff peaks. Taste and adjust salt or lemon as needed.

Transfer to a shallow bowl, use the back of a spoon to create a well in the center, and drizzle with olive oil. Sprinkle with za'atar or sumac if using. Serve warm or at room temperature with pita, vegetables, or crackers.