1/2 cup chopped onion
2 tablespoons butter
1/4 teaspoon oregano, crushed
1 can cream of mushroom soup
2 cups cooked elbow macaroni
1/2 cup chopped canned tomatoes
1 large can tuna, drained and flaked
Sauté onion in butter with oregano until tender.
Blend in soup; add remaining ingredients.
Heat, stirring occasionally.
Serve with grated Parmesan cheese.