Cook the rotini pasta according to package instructions until al dente.
In a large mixing bowl, combine the drained tuna, cherry tomatoes, cucumber, red onion, and green bell pepper.
In a separate small bowl, whisk together the olive oil, white wine vinegar, Dijon mustard, salt, and pepper.
Pour the dressing over the tuna and vegetable mixture, adding the cooked rotini pasta as well.
Fold in the chopped parsley, mixing gently until just incorporated.
Taste and adjust the seasoning as necessary before serving.
Refrigerate the salad for at least 30 minutes before serving to enhance flavors.