In a mixing bowl, combine the drained canned tuna, chopped celery, and sliced green onions. Add mayonnaise and Dijon mustard, stirring until well-coated and creamy.

Taste the tuna salad and add salt and pepper to your preference. Adjust seasoning as needed.

Lay a nori sheet flat on a clean surface, shiny side down. Ensure it stays flat while working.

Spoon a generous amount of tuna salad onto one edge of the nori sheet, leaving about an inch of space on the sides.

Starting from the edge with filling, tightly roll the nori around the salad mixture, tucking in the sides to secure it.

Using a sharp knife, slice the nori wrap in half diagonally for easier handling and serve immediately.