Combine the tomato puree, tinned tomatoes, minced onion, salt, pepper and oregano in a saucepan. Cover and simmer for 20 minutes.
Bring a large pot of lightly salted water to a boil. Add pasta and cook for 8 to 10 minutes or until al dente. Drain and rinse with cool water.
Put a layer of cooked pasta in a greased 3 litre casserole dish. After the pasta, you put in the cottage cheese and spread it out to cover all the pasta. Layer on the sauce, then another layer of pasta, then the mozzarella cheese and more sauce. Add the last layer of pasta, the parmesan and finish with a layer of sauce.