In a large pot, cook spaghetti according to package directions (under cook by 3 minutes).
If you have a sauce with meatballs in it, with large slotted spoon, scoop meatballs from sauce and set aside.
Scoop 1/2 of the cooked spaghetti (with large slotted spoon) into tomato sauce. Gently stir until pasta is fully coated with sauce.
Add this portion of the pasta with sauce to your large Pyrex bowl (or casserole).
Sprinkle on 1/2 of the cheese and some oregano.
Combine the rest of the pasta with the sauce and layer it on top of the first portion of spaghetti already in the Pyrex bowl (or casserole).
Sprinkle on the rest of the cheese, oregano and a little drizzle of extra-virgin olive oil.
If you made a sauce with meatballs, add cooked meatballs to top of spaghetti.
Bake at 375 for approx 20 minutes or until cheese is melted.