Preheat oven to 350 degrees Fahrenheit
Cook ziti according to package directions. Drain in colander and rinse lightly.
Heat oil in large non-stick skillet over medium high heat.
Saute onion until golden, about 3 minutes.
Add the ground turkey and cook until no longer pink, about 8 minutes.
Add the sauce. Bring sauce to a boil; then stir in the cooked noodles.
Place the ziti mixture in a large baking pan lightly sprayed with cooking spray.
Top with cheese and oregano.
Bake until cheese is melted and casserole is heated through, about 20 minutes. Serve hot.