In a medium mixing bowl, whisk together the mayonnaise, Dijon mustard, and lemon juice until smooth. Add salt and pepper to taste.

Open the can of chickpeas, drain them, and rinse under cold water. Pat them dry.

In a large mixing bowl, gently mash half of the chickpeas with a fork.

Add the flaked tuna, diced celery, and chopped red onion to the bowl.

Pour the dressing over the salad ingredients and fold gently.

Cover the bowl and refrigerate for at least 30 minutes before serving.