Process ginger and garlic in blender until well mashed. Mix with meat, onions, mussala, curry powder, and turmeric. Sauté in a heavy frying pan over a low heat for 30 minutes, stirring occasionally and breaking up the meat (no oil or butter is needed). Spoon off fat.
Cut sheets of thawed egg-roll dough into 3- by 6-inch strips. Fold one point up to form a triangular pocket. Fold over again and fill the pocket with some of the meat mixture. Bring down the top and seal all open sides with a paste made of flour and water. It should be a neat, secure triangle of meat-stuffed pastry.
Deep-fat fry samosas in oil until golden brown, a few at a time. Drain and keep warm.