Preheat the oven to 200 degrees F.

To make the couscous, in a medium saucepan, bring the water and butter to a boil. Gradually stir in the couscous and remove from the heat. Cover and let stand 5 minutes. Transfer the couscous to an ovenproof dish. Cover and keep warm.

In a large soup pot over medium heat, heat 2 tablespoons of the olive oil and stir in the paprika, cumin, turmeric, and pepper. Cook, stirring, until the spices give off a fragrant aroma, 1 to 2 minutes. Add the water or stock, parsley, cilantro, tomatoes, carrots, and turnips. Cover and bring to a boil. Cook until the carrots are tender, 12 to 15 minutes. Add the zucchini and peppers, and cook until tender, 8 to 10 minutes. With a slotted spoon, transfer the vegetables to an ovenproof dish. Cover and keep warm. Keep the broth simmering on the stove.

Cut the fish fillets into 3-inch pieces. In a medium skillet over medium-high heat, heat the remaining 2 tablespoons olive oil and sauté the garlic until golden, 2 to 3 minutes. Discard the garlic. Cook the fish until light brown, 1 to 2 minutes on each side. Add the fish, mussels, and shrimp to the broth in the pot. Cook until the fish begins to separate into flakes, 8 to 10 minutes. (Do not overcook.) Discard any mussels that don't open.

Mound the couscous in the center of a large, shallow serving platter. Arrange the carrot, turnip, and zucchini sticks atop the couscous like spokes of a wheel. Set the fish, shellfish, and peppers around the dish. Ladle some of the hot broth over the couscous.

Serve immediately, with prepared harissa and remaining soup broth on the side.