In a medium-sized bowl combine the tuna, mayonnaise, celery, red onion, dijon mustard, and parsley. Add salt and pepper to taste.
1 ea Small red onion, diced, 1 stalk Celery, diced, 1/2 cup Mayonaise, 1/4 cup Parsley, finely chopped, 1 tsp Dijon mustard, 10 oz Tuna