Empty cans of chickpeas into a strainer/colander and rinse, then leave to drain.
Halve the grape tomatoes and transfer to a large salad bowl.
Trim off and discard the ends of the cucumber. Quarter the cucumber lengthwise, then slice crosswise into 6mm thick pieces on an angle and add to the salad bowl.
Trim off and discard the ends of the celery. Halve the celery lengthwise, then slice crosswise at an angle into 6mm thick pieces and add to the salad bowl.
sing a knife, shave parsley leaves off the stems, then finely chop the leaves and add to the salad bowl.
Small dice the onion and add to the salad bowl.
Halve the olives and add to the salad bowl.
Add the capers to the salad bowl.
Open the cans of tuna and drain the liquid then add to the salad bowl.
If desired, dry the chickpeas with paper towel. Once dry add them to the salad bowl.
Juice the lemon into a small bowl.
Add olive oil, dijon salt, and pepper to the bowl with the lemon juice and whisk together, then pour over the salad and toss to coat.