Cook the jumbo pasta shells according to package instructions, until al dente. Drain and set aside to cool.
In a large skillet, heat a teaspoon of olive oil over medium heat. Add the chopped onion and sauté until softened, about 3-4 minutes. Add the minced garlic and cook for an additional minute.
Add the ground beef to the skillet, season with oregano, basil, salt, and pepper, and cook until browned. Drain any excess fat from the skillet.
Remove the skillet from heat and stir in ricotta cheese, half of the mozzarella cheese, and half of the Parmesan cheese. Mix until well combined.
Spread a thin layer of marinara sauce on the bottom of a 9x13-inch baking dish.
Stuff each cooked pasta shell with about 2 tablespoons of the ricotta-beef mixture and place the shells neatly in the baking dish.
Pour the remaining marinara sauce over the stuffed shells, ensuring they are well coated. Sprinkle the remaining mozzarella and Parmesan cheeses on top.
Cover the dish with aluminum foil and bake in the preheated oven for 25 minutes.
Remove the foil and bake for an additional 10-15 minutes, until the cheese is bubbly and golden brown.
Once done, remove from the oven and let it cool for a few minutes before serving. Garnish with fresh basil leaves.
Notes
Serve each portion with a dollop of extra marinara on the side and a sprinkle of fresh chopped basil for added color.