Whisk together the avocado oil, mustard, apple cider vinegar, pepper, and salt until well combined. Set aside.
In a separate bowl, mix the yogurt, lemon juice, fresh dill, and minced garlic until smooth.
Pour the prepared dressing into the yogurt sauce and stir until the two mixtures are well combined.
In a large mixing bowl, combine the drained and rinsed chickpeas, drained tuna, diced cucumber, and chopped celery. Then, add the finely diced red onion to the bowl.
Pour the creamy dressing over the salad ingredients and gently toss them until they all are evenly coated.
Taste the salad and adjust with salt and pepper according to your preference.
If time allows, refrigerate the tuna chickpea salad for about 30 minutes before serving to allow the flavors to meld.
Garnish with additional fresh dill or a lemon wedge before serving.