Preheat oven to 375°F (190°C).
Make meat sauce: Brown ground beef in a large pot. Season with garlic powder, Italian seasoning, salt, and pepper. Stir in marinara sauce and diced tomatoes. Simmer covered for 15 minutes, then taste and adjust seasoning. Reserve 2 cups of sauce aside.
Cook pasta: Meanwhile, boil the ziti in salted water until just shy of al dente. Drain.
Prepare ricotta mixture: In a bowl, mix ricotta, mozzarella, Parmesan, egg, parsley, basil, and garlic. Season to taste.
Assemble (first layer): In a 9×13 baking dish, layer half the pasta mixed with half the meat sauce. Dot with half the ricotta mixture and fresh mozzarella slices.
Top layers: Pour the reserved 2 cups of meat sauce over. Add the remaining pasta and remaining ricotta mixture.
Finish topping: Sprinkle shredded mozzarella and Parmesan on top.
Bake covered: Cover with aluminum foil (sprayed with nonstick spray) and bake 20 minutes.
Uncover & broil: Remove foil and bake another 10 minutes. Then broil 1–2 minutes until cheese is golden.
Garnish & serve: Let rest briefly, then garnish with basil or parsley before serving.