Cook the pasta shells according to the package instructions until al dente. Drain and set aside to cool slightly.
In a large skillet, heat a little olive oil over medium heat. Add the minced garlic and sauté for about 1 minute until fragrant.
Add the ground beef to the skillet, breaking it apart with a spoon. Cook until browned and cooked through, around 5-7 minutes. Season with salt, pepper, oregano, and basil.
Remove from heat and let the beef mixture cool slightly. In a mixing bowl, combine the cooked beef, ricotta cheese, half of the mozzarella, Parmesan, chopped spinach, and beaten egg. Mix until well combined.
Fill each pasta shell with the beef and ricotta mixture using a spoon.
Spread 1 cup of marinara sauce on the bottom of a large baking dish. Arrange the stuffed shells in the dish. Pour the remaining marinara sauce over the shells and sprinkle the rest of the mozzarella cheese 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, or until the cheese is bubbly and slightly golden.
Garnish with fresh parsley before serving.
Notes
Serve the stuffed shells on individual plates, with a sprinkle of extra Parmesan and a side of garlic bread for a complete meal.