Using a large skillet, cook the ground beef, onion and garlic until meat is brown and no pink is left.
Mix in the hot water, tomato paste, beef bouillon, and oregano. Simmer uncovered for 30 minutes until reduced to your desired consistency.
While the meat sauce is simmering, in a small bowl mix the cottage cheese and beaten egg with the Parmesan and one cup of the mozzarella cheeses.
Preheat the oven to 350F. Stuff the cooked pasta shells with the cheese and egg mixture and arrange them in a greased 9 x13 inch casserole dish.
Spoon the meat and tomato sauce over the pasta shells, cover with foil and bake for 30 mins. After 30 mins, remove the foil, sprinkle with the rest of the mozzarella cheese and bake 5 more minutes until the cheese is totally melted.