Heat the oven to 375°F and set a 9x13-inch baking dish nearby.

Cook the lasagna noodles in boiling water until flexible but still slightly firm, 8 to 9 minutes. Drain and lay them flat on a clean baking sheet.

Pat the shrimp dry. Melt 1 tablespoon of the butter in a large skillet over medium-high heat. Add the shrimp and cook for 2 to 3 minutes, stirring, until pink and opaque. Transfer to a bowl to cool.

Mix the ricotta, egg, half of the Parmesan, half of the parsley, lemon juice, salt, black pepper, and red pepper flakes. Gently fold in the shrimp and crabmeat.

Melt the remaining butter in a medium saucepan over medium heat. Add the garlic and cook for 30 seconds. Whisk in the flour for 1 minute, then gradually whisk in the milk and half-and-half. Simmer for 3 to 4 minutes until lightly thickened. Remove from the heat and whisk in the remaining Parmesan.

Spread about 1 cup of Alfredo sauce across the baking dish. Divide the seafood filling among the noodles, leaving a small edge clear, then roll each noodle from one short end.

Arrange the rolls seam-side down. Spoon the remaining sauce over the top and sprinkle with the mozzarella.

Cover with foil and bake for 15 minutes. Uncover and bake for 10 minutes more, until bubbling and lightly browned. Rest for 5 minutes, then scatter the remaining parsley over the top.