Preheat oven to 350. Prepare a 11 x 7" baking pan with cooking spray; set aside. Prepare pasta shells according to package directions; drain. To prepare filling combine tuna, 1/2 cup cottage cheese, parsley, onions, lemon juice, and 1/4 teaspoon dill weed in a mixing bowl. Stuff cooked pasta shells with tuna mixture and place seam side down in prepared pan. To prepare sauce, combine remaining cottage cheese, yogurt, dill weed, and garlic powder. Spoon over pasta shells. Sprinkle with parmesan cheese. Bake for 30 minutes.