In a large saucepan, saute onion in butter until tender. Stir in the tuna, soup, milk, garlic salt, oregano and pepper until combined.Spread 3/4 cupful into a greased 11-in. x 7-in. baking dish.
Layer with three noodles (trimming if necessary), 3/4 cup tuna mixture, half of the cottage cheese and a third of the mozzarella cheese. Repeat layers. Top with remaining noodles, tuna mixture and mozzarella cheese. Sprinkle with Parmesan cheese.
Bake, uncovered, at 350° for 25-30 minutes or until bubbly. Let stand for 10-15 minutes before serving. Yield: 6-8 servings.