In a small bowl whisk vinegar, olive oil, Dijon mustard, oregano, shallot, and salt together, or shake ingredients together in a salad dressing shaker.
Instructions for the salad:
Add chickpeas, tomatoes, cucumber, and olives to a bowl, pour in dressing, and gently mix together.
Tear or slice basil leaves and add to the bowl along with crumbled feta cheese, and gently mix again. Season with fresh ground pepper and more salt to taste if necessary.