Make the soup base: Heat a large heavy pot over medium-high heat. Add the olive oil, and once it is very hot, add the garlic and onion. Cook until lightly browned, 5 to 10 minutes, then add the peppers. Cook until they begin to soften, about 10 minutes, then add the carrots and cook for 5 minutes together. Add the cumin, paprika, and other spices, and cook for 1 minute more. Pour in the broth and salt, and bring to a simmer. Cover, and simmer over gentle heat until the carrots and peppers are tender, 25 to 30 minutes. Use a hand blender (or transfer to an upright blender) to purée the mixture until smooth. Add the harissa a dollop at a time, to taste. Meanwhile, make the couscous: Bring the broth or water and salt to a simmer. Stir in the couscous. Cover the pot, and remove from the heat. Let stand for 5 to 10 minutes. Right before serving, stir to fluff the couscous. To serve: Ladle the soup into bowls, and spoon a couple tablespoons of cooked couscous into the center of each, swirling it in slightly. Scatter the herbs over, and serve with lemon wedges.