Prepare meat and vegetables, cutting into cubes. Prepare marinade. In a large bowl toss steak, peppers and onions with 1/3 cup marinade and coat well. Cover and let marinate on the counter for 30-45 minutes. Reserve remaining marinade for serving.
To prepare the couscous, heat 1 tablespoon olive oil in a medium pot, add couscous, stirring to coat until toasted about 1-2 minutes. Add water/stock and salt. Bring to a boil, reduce heat to low, cover and simmer until couscous is tender about 8-10 minutes. Remove from heat and transfer to a serving bowl. Fluff with fork and let cool. Stir in 2-3 tablespoons olive oil. Just before serving add herbs, preserved lemon, lemon juice, salt and pepper. Taste and adjust seasoning as needed.
Thread each skewer with meat, peppers and onion and repeat to fill skewer. Repeat on all skewers ensuring not to overcrowd each skewer. Brush with marinade from bowl. Grill kebab on a preheated grill 8-10 minutes turning each kebab every 2 minutes until browned all sides. Transfer to serving platter. Serve with couscous and garnish with lemon wedges and remaining reserved fresh marinade sauce. Serves 4-6.