In a bowl, place tuna that has been drained of all canned-liquid. Add the celery (and/or fennel if you're using it), fresh parsley, olive oil, fresh squeezed lemon juice, pepper and salt.
Use a fork and break the tuna down and into the juices.
Combine all ingredients so that the olive oil and lemon juice have completely soaked into the tuna, and there is an even distribution of all ingredients.
Top onto bread, use as a filling for lettuce wraps, or top salad greens. Any left overs can be stored in a sealed container and kept in the refrigerator for up to three days.