Stir together yogurt, lemon juice, dill and 1/4 teaspoon garlic salt in small bowl; set aside.
Heat oil in large skillet over medium-high heat. Add chicken; sprinkle with remaining 1/2 teaspoon garlic salt. Cook 5 to 7 minutes or until chicken is no longer pink, stirring occasionally. Add drained tomatoes; heat 3 minutes more or until tomatoes are hot, stirring occasionally.
Spread yogurt mixture evenly inside pita pockets; top with cucumber slices. Divide chicken mixture evenly and spoon into pita pockets; top evenly with cheese. Serve immediately.