Mix the drained tuna in a large bowl.
Break it up with a fork for even texture.
Add the diced celery, red bell pepper, green onion, and cucumber.
Combine these ingredients gently with the tuna.
In a separate bowl, whisk together the mayonnaise, lemon juice, Dijon mustard, and Old Bay seasoning.
Ensure the dressing is well-blended.
Pour the dressing over the tuna mixture.
Stir everything together until all the ingredients are evenly coated.
Refrigerate the tuna salad for at least one hour before serving.
This allows the flavors to meld beautifully.