Preheat oven to 375 degrees. Place squash on a baking sheet lined with parchment. Drizzle with 1 1/2 tablespoons olive oil and salt and pepper. Toss well and roast until golden brown, 45 to 50 minutes.
In a large skillet or pot, warm remaining 1 1/2 tablespoons olive oil over medium-high heat. Add onions and a pinch each of salt and pepper. Cook for 3 to 4 minutes. Stir in garlic and cook for 3 minutes. Stir in parsley stems, cumin, and paprika, and cook for 1 minute. Add carrots and 1 cup chickpea cooking liquid (or water, if using canned chickpeas) to onion mixture. Bring to a boil over high heat. Reduce heat to low and simmer, covered, until carrots are tender, 10 to 12 minutes.
Add tomatoes and chickpeas. Raise heat to medium-high and simmer for 10 minutes. Stir in harissa paste, chopped parsley leaves, roasted squash, and remaining 1/2 cup chickpea cooking liquid (or water). Simmer, uncovered, until flavors meld, another 3 minutes. Season with salt and pepper to taste.