Preheat oven to 425°F. Toss butternut squash with 1 Tbsp. of the oil, 1/2 tsp. of the salt, and 1/4 tsp. of the black pepper. Spread on a baking sheet and roast for 35 minutes, tossing once halfway through. Let cool 10 minutes.
Set aside 1/2 cup of the roasted butternut squash and 1/4 cup of the chickpeas. Add remaining butternut squash, chickpeas, tahini, harissa paste, lemon juice, garlic, and remaining 1/2 tsp. salt and 1/4 tsp. black pepper to a food processor. Blend on high until smooth, gradually streaming in 2 Tbsp. olive oil.
Transfer hummus to a serving bowl. Garnish with remaining 1/2 cup roasted butternut squash, 1/4 cup chickpeas, and pomegranate arils. Drizzle remaining 1 Tbsp. olive oil overtop.