Combine the chickpeas with 5 cups water, 1 tablespoon of the olive oil, the bay leaves, and kombu in a Dutch oven or heavy stockpot over high heat. Bring to a boil, then reduce the heat to low, cover, and cook until the chickpeas are tender, about 1 hour.

Preheat the oven to 400°F.

While the chickpeas are cooking, cut the bread into thick slices, then tear the slices into bite-size pieces. Place the bread in one layer on a large rimmed baking sheet and toast until crisp and lightly browned on top, about 10 minutes. Remove from the oven and let cool in the pan.

Pour another 2 tablespoons of the oil into a large skillet over medium-high heat. When it shimmers, stir in the onion and garlic and sauté until tender and starting to brown, 6 to 8 minutes. Stir in 1 tablespoon of the cumin, the salt, and tomato paste and sauté until fragrant, about 30 seconds. Turn off the heat.

When the chickpeas are tender, remove and discard the bay leaves and kombu. Use a slotted spoon to transfer 2 cups of the chickpeas to a blender and a measuring cup to transfer ½ cup of the chickpea cooking liquid to the blender. Add the remaining ¼ cup of the olive oil and puree liquid to the blender. Return the puree to the soup and stir in the onion mixture to combine. Return the puree to the soup and stir in the onion mixture to combine. Return the puree to the soup and as much of the pan juices as possible. If it seems too thick, add a little more water until it reaches your preferred consistency.

Stir in 1 tablespoon of the harissa and the lemon juice. Taste and add more salt if needed.

To serve, divide the toasted bread pieces among soup bowls. Top each with a small dollop of harissa (more if you want things spicier), then ladle in the soup. Garnish with parsley, lemon zest, a sprinkle of cumin, and roasted chickpeas, if desired. Serve hot.

The soup can be covered and stored, without the bread, in the refrigerator for up to 1 week or in the freezer for up to 3 months.