In a large skillet, cook beef, onion and garlic over medium heat, crumbling beef, until meat is no longer pink; drain. Stir in water, tomato paste, bouillon and oregano. Reduce heat; simmer, uncovered, for 30 minutes. , Meanwhile, combine egg, cottage cheese, 1 cup mozzarella and Parmesan cheese. Stuff shells with cheese mixture., Preheat oven to 350°. Arrange shells in a greased 13x9-in. or 3-qt. baking dish. Pour meat sauce over shells. Cover; bake 30 minutes. Uncover; sprinkle with remaining mozzarella cheese. Bake until cheese is melted, about 5 minutes longer.