Boil the eggs until hard-boiled, then cool in an ice bath, peel, and chop to your preferred texture (chunky or fine).
Drain the tuna really well to prevent watery salad. Flake it with a fork in a mixing bowl.
Add mayonnaise, mustard, a small squeeze of lemon (or a splash of pickle juice), salt, pepper, and any optional seasonings like garlic powder or paprika. Mix until creamy.
Fold in chopped eggs, celery, onion, and pickles/relish if using. Stir gently so the eggs stay a little chunky and the salad doesn’t turn paste-like.
Taste and adjust—more mustard for bite, more lemon/pickle juice for tang, more pepper or cayenne for heat.
Cover and chill for 20–30 minutes if you can. Serve cold in sandwiches, wraps, lettuce cups, or with crackers and cucumber slices.