Cook spaghetti and set aside. Preheat oven to 220°C.
In a saucepan, brown onion then add mince and brown also.
Add tomatoes, oregano, salt and pepper to taste.
Add about 2 cups of water and stir.
Turn heat down to about medium and cook mince for about 20 to 30 minutes or until most of the liquid has been evaporated. Stir occasionally then turn stove off and leave.
Make béchamel sauce by melting butter in another saucepan, remove from stove, add flour and stir in. Add milk and stir well.
Return to stove and stir continuously until sauce boils and thickens. Add a pinch of salt.
In a baking dish layer as follows: sprinkle of cheese; half of the pasta; sprinkle of cheese; all of the mince mixture; sprinkle of cheese; rest of pasta; sprinkle of cheese; and all of béchamel sauce.
At this point stab and wiggle a knife in several places of the dish so that the sauce goes to the bottom, then end with rest of parmesan cheese.
Bake in the oven for about 30 to 40 minutes or until top is golden brown.