Ingredient Note: Tahini is a smooth, thick paste made from ground sesame seeds and commonly used in Middle Eastern foods. Look for it in the Middle Eastern section or near other nut butters in large supermarkets.
To prepare burgers: Place chickpeas, scallions, egg, flour, oregano, cumin and 1/4 teaspoon salt in a food processor. Pulse, stopping once or twice to scrape down the sides, until a coarse mixture forms that holds together when pressed. (The mixture will be moist.) Form into 4 patties.
Heat oil in a large nonstick skillet over medium-high heat. Add patties and cook until golden and beginning to crisp, 4 to 5 minutes. Carefully flip and cook until golden brown, 2 to 4 minutes more.
To prepare sauce & serve: Meanwhile, combine yogurt, tahini, lemon juice, parsley and 1/4 teaspoon salt in a medium bowl. Divide the patties among the pitas and serve with the sauce.