Bring a large pot of salted water to a boil. Add the 20 large pasta shells and cook until just al dente, about 8-10 minutes. Drain and rinse under cold water to stop the cooking process. Set aside on a baking sheet to prevent sticking.
Heat 2 tablespoons olive oil in a large skillet over medium heat. Add the minced garlic and sauté for 30 seconds until fragrant. Toss in the peeled and deveined shrimp along with 1 teaspoon Italian seasoning, salt, and pepper. Cook shrimp until pink and opaque, about 2 minutes per side. Remove from heat and chop into bite-sized pieces.
In the same skillet, pour in 2 cups heavy cream and bring to a gentle simmer over medium-low heat. Stir in 1/2 cup grated Parmesan cheese until melted and smooth. Season with salt and pepper to taste. Remove from heat and set aside.
In a mixing bowl, combine 1 cup ricotta cheese, 1 cup grated mozzarella cheese, chopped shrimp, and a few spoonfuls of Alfredo sauce. Mix gently to blend everything together without breaking up the shrimp too much.
Carefully spoon the shrimp and cheese filling into each cooked pasta shell, arranging them in a greased 9x13 inch baking dish.
Pour the remaining Alfredo sauce evenly over the stuffed shells. Sprinkle additional mozzarella and Parmesan on top if desired. Cover with foil and bake at 375°F (190°C) for 25 minutes. Remove foil and bake for another 5-10 minutes until the cheese is golden and bubbly.
Sprinkle freshly chopped parsley over the baked shells for a burst of color and freshness. Serve hot and enjoy the rich, creamy flavors of this delectable pasta dish.