Falafel-Spiced Tomatoes and Chickpeas on Flatbread

Name: Falafel-Spiced Tomatoes and Chickpeas on Flatbread
Cuisine: Asian, Middle Eastern
Ingredients: 2 garlic cloves, finely chopped; 1 teaspoon sumac; 1/2 teaspoon crushed red pepper flakes; 1/2 teaspoon ground coriander; 1/2 teaspoon ground cumin; 1 teaspoon kosher salt, plus more; 2 large heirloom tomatoes, any color, thinly sliced; 1 (15.5–ounce) can chickpeas, rinsed; 2 tablespoons red wine vinegar; Freshly ground black pepper; 1 small shallot, thinly sliced; 1/2 cup parsley leaves with tender stems; 3 tablespoons olive oil; 1 Persian cucumber, peeled, chopped; 3/4 cup plain yogurt; 1/2 cup coarsely chopped fresh mint; 1/2 cup coarsely chopped fresh parsley; Kosher salt, freshly ground pepper; Flatbread and assembly; 2 teaspoons kosher salt; 3/4 teaspoon baking powder; 1/2 teaspoon sugar; 2 cups all-purpose flour, plus more for surface; 1 cup plain yogurt; 4 tablespoons olive oil, plus more for drizzling; Sumac, a tart, citrusy spice, can be found at Middle Eastern markets and specialty foods stores