Preheat oven to 425°F and line a baking sheet with parchment paper.
Place the chickpeas onto the prepared baking sheet and drizzle with the olive oil, salt, pepper, garlic, onion, Zaatar, and red pepper flakes until well-combined. Bake until the chickpeas are crispy and golden, about 18 to 20 minutes, tossing about halfway through baking. Remove from the oven and allow to cool.
In the meantime, to make the dressing, in a large bowl, whisk together the pickle juice, olive oil, mustards and dill until smooth and well combined. Season with a pinch of salt and pepper to taste.
To assemble the salad, transfer the crispy chickpeas into a large bowl. Add the radishes, pickles, celery, red onions, scallions, and half of the herbs and feta. Drizzle in the dressing and toss gently until everything is well combined. Cover with plastic wrap and chill in the fridge for at least 4 hours or overnight. Top with the remaining herbs and feta before serving. Enjoy!