01 - Preheat oven to 375°F. Position the rack in the center of the oven.
02 - Roll out the pie crust and carefully fit it into a 9-inch pie dish. Trim any overhanging dough and flute the edges decoratively. Prick the bottom gently several times with a fork to prevent bubbling. Set aside.
03 - In a large skillet over medium heat, warm the olive oil. Add the ground beef and cook, breaking it apart with a spatula, until evenly browned and cooked through, approximately 5 to 7 minutes. Drain any excess fat if needed.
04 - Add the diced onion and minced garlic to the skillet with the beef. Cook until softened and fragrant, about 3 minutes. Stir in the marinara sauce, dried oregano, salt, and pepper. Bring to a gentle simmer and cook for 5 minutes to allow the flavors to meld. Remove from heat.
05 - In a medium mixing bowl, combine the ricotta cheese, egg, 1 cup of the mozzarella, Parmesan, chopped basil, and red pepper flakes. Stir until smooth and well blended.
06 - Spread half of the meat sauce evenly across the bottom of the prepared crust. Dollop the ricotta mixture over the sauce and gently spread it into an even layer. Top with the remaining meat sauce. Sprinkle the remaining 1 cup of mozzarella evenly over the top.
07 - Loosely tent the pie with aluminum foil. Bake for 30 minutes. Remove the foil and continue baking for an additional 15 minutes, until the cheese is golden brown and bubbly.
08 - Allow the pie to cool for 10 minutes before slicing to set the layers. Serve warm, garnished with additional fresh basil if desired.