Step 1: Cook the Pasta Shells

1. Bring a large pot of salted water to a boil.
2. Add the jumbo pasta shells and cook until al dente, following package instructions (usually about 9–10 minutes).
3. Drain the shells and rinse them under cold water to stop the cooking process.
4. Arrange the cooled shells on a greased baking sheet to prevent sticking.

Step 2: Prepare the Seafood Filling

1. In a large mixing bowl, combine the crabmeat, chopped shrimp, mozzarella cheese, mayonnaise, and beaten egg.
2. Add the finely chopped celery, green bell pepper, and red onion for texture.
3. Season the mixture with seafood seasoning, black pepper, and lemon juice (if desired).
4. Mix everything thoroughly until evenly combined.

Step 3: Make the Parmesan Cheese Sauce

1. In a medium saucepan, melt the butter over medium heat.
2. Whisk in the flour and cook for 1–2 minutes, stirring constantly to form a roux.
3. Gradually pour in the milk, whisking constantly to avoid lumps.
4. Bring the mixture to a gentle boil and cook until thickened, about 2–3 minutes.
5. Remove from heat and stir in the grated Parmesan cheese, salt, pepper, and garlic powder (if using).

Step 4: Assemble the Seafood Stuffed Shells

1. Preheat your oven to 350°F (175°C).
2. Grease a 9×13-inch baking dish with butter or non-stick spray.
3. Take each cooked shell and stuff it with about 1 tablespoon of the seafood filling.
4. Arrange the filled shells snugly in the baking dish.
5. Pour the Parmesan cheese sauce evenly over the stuffed shells, ensuring all shells are well-coated.

Step 5: Bake the Dish

1. Cover the baking dish with aluminum foil and bake for 20 minutes.
2. Remove the foil and bake uncovered for an additional 10–15 minutes, or until the sauce is bubbly and golden on top.
3. If desired, sprinkle with toasted breadcrumbs and chopped parsley for garnish before serving.

Step 6: Serve and Enjoy

1. Let the seafood stuffed shells cool for 5 minutes before serving to allow the flavors to settle.
2. Serve with your favorite side dishes, such as a crisp garden salad or garlic bread, and enjoy!