Heat grill to medium-high. In a large bowl, toss the chicken with 1 tablespoon oil, then the coriander, oregano and ¼ teaspoon each salt and pepper. Thread onto skewers.
Place the tomatoes and garlic on a large piece of heavy-duty foil. Drizzle with 1 tablespoon oil and sprinkle with ¼ teaspoon each salt and pepper. Fold and seal the foil to form a pouch.
Place the pouch and skewers on the grill and cook, shaking the pouch and turning the kebabs occasionally, until the chicken is cooked through, 8 to 10 minutes. Just before removing from the grill, brush the chicken with 1 tablespoon lemon juice.
Meanwhile, in a large bowl, toss the lettuce, scallions, and dill with the remaining 2 tablespoons lemon juice and tablespoon oil, plus ¼ teaspoon each salt and pepper. If desired, grill the pita bread until warm, about 1 minute per side.
Spread the pita with yogurt, if desired, then stuff with the chicken, tomatoes, and salad.
