Start by thinly slicing the red onion and placing it in a bowl with lemon zest, lemon juice, and salt. Let it sit for a few minutes to soften and mellow. This step reduces sharpness and builds a flavorful base.
Drain and rinse the chickpeas and butter beans thoroughly. Add them to a large bowl along with chopped olives, artichoke hearts, mint, and parsley. Toss gently so everything is evenly distributed.
Heat olive oil in a small skillet over low heat and add the chopped garlic. Cook briefly until fragrant but not browned. Remove from heat and stir in za’atar, sumac, and cumin to release their aroma.
Pour the warm marinade over the bean mixture and toss gently to coat. Mix in the softened onions along with their lemony juices. Cover and refrigerate for at least two hours to allow flavors to deepen.
Before serving, taste and adjust salt if needed. Serve chilled or at room temperature for the best flavor and texture. The longer it sits, the more delicious it becomes.