In a small bowl, add mayo, lemon juice, sugar, salt,and pepper to form your dressing.
Mix until well combined.
Drain your canned tuna, add it to a separate bowl, and use a fork to break your tuna into smaller pieces.
Next, add in your diced celery, red onion, and your dressing to your tuna.
Mix until well combined.
Refrigerate for a minimum of 1 hour and enjoy.