In a bowl, soak the bread in the milk for a few minutes until softened, then squeeze out excess liquid and transfer to a food processor; pulse to grind. Place in a large bowl; add the lamb, egg, cheese, one-quarter of the garlic, the lemon peel and allspice; season with salt and pepper. Grate about 2 tablespoons of the onion into the lamb. Combine the mixture and roll into meatballs the size of walnuts (20 to 25 balls).
In a deep skillet, heat the EVOO, 3 turns of the pan, over medium heat. Add the remaining garlic, grate in the remaining onion and cook until softened, about 3 minutes. Stir in the tomatoes and 1/2 cup chicken broth and cook until bubbling. Add the meatballs and simmer, turning over if theyre not fully submerged, until cooked through, about 8 minutes. Stir in the parsley and mint and season to taste with salt and pepper.
Meanwhile, in a small saucepan, bring the remaining 1-1/2 cups chicken broth and the butter to a simmer. Stir in the couscous, turn off the heat, cover and let stand for 5 minutes. Add the pine nuts and fluff with a fork.
Serve the meatballs and sauce over the couscous.