Drain the tuna in a fine-mesh strainer, pressing firmly with the back of a spoon to squeeze out as much liquid as possible.
Transfer the tuna to a medium bowl and flake it with a fork to your preferred texture. Sprinkle with the lemon juice, salt, and pepper; toss and let stand 5 minutes.
Add the mayonnaise and Dijon mustard. Fold gently until the tuna is evenly coated — do not overmix.
Fold in the celery, red onion, pickles, and herbs until just combined.
Taste and adjust salt, pepper, and lemon. For the best flavor, cover and chill 30 minutes before serving.