Preheat the oven to 325°. In a large enameled cast-iron casserole, heat 2 tablespoons of the oil. Season the shanks with salt and pepper. Add them to the casserole, 2 at a time, and cook over moderately high heat until browned all over, about 12 minutes. Transfer to a plate and wipe out the casserole.
Heat the remaining 2 tablespoons of oil in the casserole. Add the onion, carrots and garlic and cook over moderate heat, stirring, until lightly browned, about 5 minutes. Add the cumin, coriander, cinnamon, allspice and nutmeg and cook, stirring until lightly toasted, about 1 minute. Add the tomato paste and harissa and cook over moderately high heat, stirring, until lightly browned, about 2 minutes. Stir in the wine and boil until reduced to a thick syrup, about 4 minutes.
Add the tomatoes and 1 cup of the chicken stock to the casserole. Season with salt and pepper and bring to a boil. Nestle the lamb shanks in the liquid. Cover tightly and braise in the oven for about 3 hours, basting occasionally, until the meat is almost falling off the bone. Transfer the shanks to a platter and cover with foil. Leave the oven on.
Spread the almonds in a pie pan in an even layer and toast for about 10 minutes, or until golden.
Strain the sauce into a bowl, pressing on the vegetables; skim any fat. Return the sauce to the casserole and boil over high heat until reduced to 1 cup, about 10 minutes. Return the vegetables and lamb to the sauce and keep warm.
In a small bowl, mix the mint with the cilantro and almonds and season lightly with salt and pepper.
Melt the butter in a medium saucepan. Add the shallot and cook over moderately high heat until softened, about 2 minutes. Stir in the couscous and cook until lightly browned, 2 to 3 minutes. Add the remaining 1 cup of chicken stock, the water and 1/4 teaspoon of salt and bring to a boil. Remove from the heat and add the currants. Cover and let stand for 10 minutes. Fluff with a fork and stir in half of the herb-almond mixture.
Mound the couscous in the center of a large platter. Arrange the lamb shanks around the couscous and spoon the sauce on top. Sprinkle with the remaining herb-almond mixture and serve.
Make Ahead: The lamb can be refrigerated for up to 3 days. Rewarm gently.
Wine Recommendation: The warmly flavored spices, the luscious braised lamb and the sweet toasted almonds are all a great match for the hit of fruit in the 1999 Howell Mountain Vineyards Zinfandels--Old Vines, the Beatty Ranch and the Black Sears.