Bring a large pot of salted water to a boil. Add pasta and cook according to package instructions until al dente, roughly 8–10 minutes. Drain and rinse under cold water.

If using fresh shrimp, boil until pink and opaque for about 2–3 minutes. For pre-cooked shrimp, chop into bite-sized pieces.

Dice celery, red bell pepper, and red onion into small pieces. Finely chop fresh parsley for garnish.

Whisk mayonnaise, sour cream, Dijon mustard, and lemon juice in a mixing bowl until smooth. Add Old Bay seasoning, salt, and pepper, stirring to combine.

In a large bowl, add cooled pasta, shrimp, imitation crab, and diced veggies. Pour dressing over and toss until well combined.

Cover and refrigerate for at least 1 hour to let flavors meld.

Transfer to a serving dish, garnishing with fresh parsley and paprika if desired. Serve over lettuce if preferred.