Cook the shells: Boil the jumbo shells until al dente. Drain and set aside.
Prepare the filling: Heat olive oil in a pan. Sauté onion and garlic until fragrant. Add ground beef and cook until browned. Stir in tomato paste, tomato sauce, oregano, salt, pepper, and chili flakes. Simmer for 10 minutes.
Stuff the shells: Spoon the beef mixture into the cooked shells.
Layer the lasagna: In a baking tray, spread a thin layer of béchamel sauce. Add stuffed shells, cover with more béchamel, and sprinkle generously with Parmigiano and mozzarella.
Bake: Preheat oven to 375°F (190°C). Bake for 25–30 minutes until golden and bubbly.
Serve hot: Garnish with fresh parsley or basil and enjoy with your favorite drink (and beats).