Prepare a large pot of salted water and bring it to a rolling boil. Add pasta shells and cook for about 9 to 11 minutes, then drain and cool on a baking sheet.

In a mixing bowl, combine ricotta cheese, half of the mozzarella, Parmesan cheese, shrimp, scallops, crab meat, minced garlic, parsley, lemon zest, salt, and pepper. Mix until well combined.

In a medium saucepan, heat olive oil and sauté minced garlic until fragrant. Add heavy cream and marinara sauce, stirring well. Simmer for approximately 8 minutes.

Preheat oven to 375°F (190°C). Spread a layer of sauce in a baking dish. Fill each cooled shell with the seafood mixture and place seam-side up.

Pour remaining sauce over shells and sprinkle with remaining mozzarella. Cover with foil and bake for 25 minutes, then uncover and bake for an additional 10-15 minutes.

Let the stuffed shells rest for about 5 minutes before serving. Garnish with additional parsley.