In a small mixing bowl, whisk together ½ cup of mayonnaise, 1 tablespoon of Dijon mustard, and the juice of half a lemon until smooth. Add salt and pepper to taste and set it aside.

Open a can of chickpeas, rinse thoroughly under cold water, and pat them dry.

In a medium bowl, add the prepared chickpeas and gently mash about half of them with a fork, leaving some whole.

Combine the mashed chickpeas with the drained tuna, diced celery, and finely chopped red onion. Add optional add-ins if desired, and pour the dressing over the mixture, stirring gently.

Let the chickpea tuna salad chill in the refrigerator for at least 30 minutes before serving.