Heat olive oil in a sauce pan over medium heat and add onion and garlic. Soften for about 3-4 minutes. Add ground beef and brown. Drain fat leaving a bit for flavor. Add tomato sauce, tomato, oregano, chili flakes, and season with salt and pepper to taste. Simmer for about 20 minutes
Bring a large pot of water to a boil and cook ziti until just before al dente. Drain and rinse with cold water to stop cooking.
In a large bowl, add ricotta, egg, Parmesan, 2/3 of the mozzarella, parsley, and salt and pepper to taste. Coarsely mix.
Preheat oven to 375. In your empty pasta pot, add half the ricotta mixture and half the pasta and toss. Add a bit of the meat sauce and toss. Add to casserole dish and top with half the meat mixture. Repeat for remaining ingredients. Sprinkle with remaining mozzarella and bake fore 20 minutes.