Place ground meat mix and water in a saucepan. Cover and cook over low heat 15 minutes; stirring occasionally. Break up with a fork. Cover and cook 5 minutes more. Drain. Meanwhile, spread one side of each tostado shell with refried beans; set aside. Put cheese and taco seasoning mix in a plactic seal bag and shake vigorously to coat cheese. To assemble, place 1 tostado shell, bean side up, on a serving dish. Layer 1/4 cup meat mixture, a little lettuce and 2 tablespoons cheese mixture over bean layer of each. Place second tostado shell atop. Repeat meat, lettuce, and cheese layers. Serve.