01 - Preheat the oven to 375°F. Roll out the pie crust and gently press it into a 9-inch pie dish. Trim any overhanging dough and flute the edges. Prick the bottom lightly with a fork to prevent puffing. Set the lined dish aside.
02 - Heat olive oil in a large skillet over medium heat. Add the ground beef and cook, breaking it apart with a wooden spoon, until evenly browned and no pink remains, about 5 to 7 minutes. Drain any excess fat from the pan.
03 - Add the diced onion and minced garlic to the browned meat. Sauté until the onion is softened and translucent, about 3 minutes. Pour in the marinara sauce, dried oregano, salt, and pepper. Stir to combine and let the sauce simmer gently for 5 minutes. Remove from heat and set aside.
04 - In a medium mixing bowl, combine the ricotta cheese, egg, 1 cup of the shredded mozzarella, Parmesan cheese, chopped basil, and red pepper flakes. Stir until the mixture is smooth, creamy, and well blended.
05 - Spread half of the meat sauce evenly across the bottom of the prepared pie crust. Spoon the ricotta mixture over the sauce in dollops, then gently spread it into an even layer. Top with the remaining meat sauce, then finish by sprinkling the remaining 1 cup of mozzarella evenly over the surface.
06 - Loosely tent the pie with aluminum foil and bake for 30 minutes. Carefully remove the foil and continue baking for an additional 15 minutes, or until the cheese is golden brown and bubbling. Allow the pie to rest for 10 minutes before slicing to let the layers set. Serve warm, garnished with additional fresh basil if desired.