Preheat your oven to 350°F (175°C).
In a large pot, bring water to a boil and cook the jumbo pasta shells according to package instructions until al dente. Drain and set aside.
In a skillet over medium heat, add the ground beef. Cook until browned, breaking it up with a spatula, about 5-7 minutes. Drain excess fat.
Add the minced garlic, Italian seasoning, salt, and black pepper to the skillet with the beef. Stir for 1-2 minutes until fragrant.
In a mixing bowl, combine the cooked beef mixture, ricotta cheese, 1 cup of mozzarella cheese, and Parmesan cheese. Mix until well blended.
Spread 1 cup of marinara sauce evenly across the bottom of a baking dish.
Stuff each cooked pasta shell with the beef and cheese mixture and place them in the baking dish.
Pour the remaining marinara sauce over the stuffed shells. Sprinkle additional mozzarella cheese on top.
Cover the baking dish with aluminum foil and bake in the preheated oven for 20 minutes.
Remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and golden.
Remove from the oven and let it rest for a few minutes. Garnish with fresh basil if desired before serving.