Preheat oven to 400°F. Line a large baking sheet with foil and mist with cooking spray. In a food processor, combine chickpeas, onion, 1/2 cup cilantro and 1/2 cup parsley. Pulse until roughly chopped. Add egg, 1/4 cup panko, cumin, coriander, pepper and salt. Pulse until mixture forms a chunky puree. Transfer to a large bowl. If mixture appears too wet, mix in additional panko as needed.
Sprinkle flour onto a small plate. Scoop out 2 tbsp chickpea mixture and form into a circular 1/2-inch-thick patty. Lightly press both sides into flour, shake off excess and place on prepared baking sheet. Repeat with remaining chickpea mixture, making a total of 12 patties. Lightly mist tops of patties with cooking spray. Bake until bottoms are golden brown, about 12 minutes. Turn patties and bake until opposite sides are golden, 5 to 7 minutes more. Cool at room temperature and refrigerate in an airtight container (MAKE AHEAD: Prepare up to 3 days in advance through Step Two.)
Meanwhile, in a small bowl, stir together cheese, yogurt, lemon juice and remaining 1 tbsp each cilantro and parsley. (MAKE AHEAD: Yogurt sauce can be made up to 3 days ahead and refrigerated in an airtight container; stir well before serving.)
Assemble sandwiches just before serving: Cut each pita in half crosswise to form 2 pockets. Stuff each pocket with 3 patties (cutting patties to fit if necessary), 1/2 cup lettuce, 2 or 3 tomato slices and a generous 1/4 cup yogurt sauce.