In a large mixing bowl, combine the cooked shrimp and crab meat.

Add the diced celery, red bell pepper, and cucumber to the seafood mixture.

In a separate bowl, whisk together mayonnaise, lemon juice, Dijon mustard, olive oil, salt, and black pepper.

Pour the dressing over the seafood and vegetable mixture and toss gently to combine. Garnish with chopped parsley and serve immediately.