In a small bowl, whisk together ? cup mayonnaise, ? cup sour cream, 2 tablespoons sweet pickle relish, 1 tablespoon white vinegar, ¼ teaspoon salt, ¼ teaspoon pepper, and ½ teaspoon dried dill.
Set the dressing aside.
Cook 16 ounces rotini pasta al dente according to the package directions.
Drain the pasta and rinse it under cold water to stop the cooking process. Allow the pasta to drain completely.
In a large mixing bowl, combine the cooked pasta, 6 ounces drained canned tuna, ½ cup diced celery, 3 sliced green onions, ¾ cup defrosted and drained frozen peas, and 1 cup diced cheddar cheese if using.
Pour the prepared dressing over the pasta mixture and stir until everything is evenly coated.
Cover and refrigerate the pasta salad for at least 1 hour before serving.