Heat the oven to 350 degrees. Coat an 11×7-inch baking dish with non-stick cooking spray.
Cook the pasta according to the package directions and drain. Cool under cold running water and drain well.
Meanwhile, combine 1 cup cottage cheese, shrimp, crabmeat, spinach, egg, and dill in a medium bowl. Spoon the filling into the shells; place in a baking dish.
Heat the butter in a medium saucepan over low heat until melted. Add the garlic, cook for 30 seconds or until fragrant, stirring constantly. Whisk in the flour; cook for 30 seconds. Whisk in 1 1/2 cups cottage cheese and the half-and-half. Bring to a boil over medium heat. Stir in the tomatoes, 1/4 cup of the Parmesan cheese and all of the remaining ingredients. Simmer over low heat for 3 minutes.
Pour over the pasta shells; sprinkle with the remaining 1/2 cup Parmesan cheese.
Bake for 35 to 40 minutes or until lightly browned and bubbly. Let stand for 10 minutes before serving.