Cook macaroni according to package direction until tender, drain.
Saute onion in small amount of olive oil, add ground round and brown well.
Stir in tomato sauce, salt, pepper, and oregano, simmer for several minutes.
Pour into a 2 quart greased casserole. Press down.
Toss macaroni with cheese, arrange on top of meat mixture, packing down.
Pour beaten eggs over macaroni and cheese.
Pour milk over eggs.
Bake in 350 degree oven for 1 hour until golden brown.
Let stand 15 minutes.
Loosen around edges with spatula.
Place plate over casserole. turn over gently to unmold. Serve in wedges.