In a large bowl, mix together chickpeas, dijon mustard, olive oil, cumin, lemon, lemon zest, salt and pepper. For best flavor, let that all sit together for at least 30 minutes in the fridge.
Toss in the rest of the chopped veggies. Taste and adjust seasonings -- adding more salt, pepper, lemon, dijon, to your liking.
Can be stored in the refrigerator for a couple of days.