Slice each potato into thick rounds, alternating between cuts that go almost through and cuts that go fully through to create pockets. Each potato should yield about 3 pieces. Soak in salted water for 20 minutes, then drain and dry well.
In a food processor, finely chop the onion, cilantro, half potato, and garlic. Combine with the ground beef, breadcrumbs, spices, salt, and oil. Mix until uniform. Cover and refrigerate.
Stuff each potato pocket with the meat mixture, pressing gently to seal.
Whisk eggs with tomato paste in a bowl and place flour in a second bowl. Heat a wide skillet with about 1 cup vegetable oil over medium heat. Dredge potatoes in flour, then egg, and fry until golden on all sides. Transfer to paper towels.
Heat oil in a wide pot over medium heat. Add garlic and cook until fragrant, about 1 minute. Lower heat, add spices, and stir briefly. Add tomatoes and water; bring to a boil. Add potatoes, arranging snugly so they are nearly submerged.
Cover and simmer on low until the potatoes are tender, about 40 minutes. Sprinkle with cilantro and cook 5 minutes more. Serve hot, preferably with couscous.