Bring a large pot of salted water to a rolling boil. Add the pasta shells and cook for 9 to 11 minutes until al dente, stirring occasionally. Drain and rinse under cool water.

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

Heat olive oil in a large skillet over medium heat. Add minced garlic and sauté for about 1 minute until fragrant. Pour in the heavy cream, stir frequently, and let simmer for 5 minutes. Stir in marinara sauce and let cook for another 3 minutes.

Preheat the oven to 375°F (190°C). Spread a thin layer of marinara sauce on the bottom of a baking dish.

Fill each shell with the seafood mixture and place seam-side up in the baking dish on marinara sauce. Pour remaining sauce over and sprinkle with leftover mozzarella.

Cover with aluminum foil and bake for 25 minutes. Remove foil and bake for an additional 10 to 15 minutes until golden brown.

Let it rest for 5 minutes before serving warm.