Combine rice, oregano and pepper in bottom of 1 1/2 quart microwaveable bowl. Stir in tomato sauce. Layer onion and tuna over rice. Heat soup, milk and cheese until cheese melts. Pour over tuna. Heat in microwave on high for 5 to 6 minutes.

milk, and cheese, pour it over the tuna and rice, and bake at 350° for 25 to 30 minutes.