For the cabbage rolls: Core the head of cabbage and boil in salted water until soft, about 5 minutes. Transfer to an ice-cold bowl of water to stop cooking. Remove from ice water, separate the green leaves and set aside for the rolls. Thinly slice the remaining cabbage and set aside for the sauce.
In a large bowl, combine the minced lamb, onion, breadcrumbs, egg, cilantro, ginger, chile pepper, garlic, salt, and pepper. Mix well, season, cover, and keep in the refrigerator until ready to use.
Preheat the oven to 350 degrees F.
Remove any thick veins from the cabbage leaves with a sharp knife. Place 1 cabbage leaf on a cutting board, add 2 tablespoons of the filling, fold sides, and roll up. Hold the loose end of the leaf with small bamboo sticks if necessary. Repeat with other leaves. Transfer the stuffed rolls into a 13 by 9-inch oven-safe dish. Keep in the refrigerator until ready to cook.
For the sauce: In a saucepan, heat the olive oil. Add onions and reserved sliced cabbage and saute until caramelized, about 10 minutes. Add garlic and ginger, continue to cook for a minute over low heat. Add the tomatoes and veal stock. Season with salt and pepper. Simmer until the sauce thickens, about 15 minutes.
Pour the sauce over the cabbage rolls and cook in the oven for 50 minutes.
For serving: Plate 2 cabbage rolls per person, and a ladle of sauce. Garnish with crumbled feta. Serve with the roasted potatoes and chive sour cream.