Middle Eastern Chickpea Platter

Name: Middle Eastern Chickpea Platter
Ingredients: 1 tablespoon extra-virgin olive oil; 1/4 cup crumbled feta; 1/4 cup halved pitted briny black olives, such as Kalamata (optional); 2 tablespoons tahini, (see Note); 4 whole-wheat pita breads, warmed and cut in half or into wedges; 2 medium tomatoes, sliced; 1/2 medium red onion, thinly sliced; 1 15- or 19-ounce can chickpeas or cannellini beans, rinsed (see Tip); 1 small eggplant, (about 12 ounces), cubed; 3 tablespoons chopped fresh parsley, plus more for garnish; 2 cloves garlic, minced; 3 tablespoons lemon juice; 1/4 teaspoon salt, divided; 1 tablespoon water