Thinly slice the onion and add it to a large bowl, tossing it together with kosher salt, lemon juice, and lemon zest. Set aside to mellow the onion.
Drain and rinse both cans of beans, then roughly chop the olives and finely mince the herbs before adding everything into the bowl with the onions.
In a pan, heat olive oil over medium heat while adding smashed garlic cloves until they just begin to brown. Remove from heat and sprinkle in za’atar, sumac, and cumin.
Pour the marinade over the bean mixture in the bowl and gently toss everything together until well combined. Adjust for salt if necessary.
Serve the salad on top of toasted sourdough bread slathered with labneh or ricotta cheese.
Store in an airtight container for up to one week, but expect some loss of crunchiness after day four.