Preheat oven to 350°F. Lightly coat twelve 2 1/2-inch muffin cups with cooking spray. On a work surface, lightly coat one sheet of phyllo dough with cooking spray (keep remaining phyllo covered with plastic wrap to prevent it from drying out). Top with another sheet of phyllo and lightly coat with cooking spray. Repeat layering two more times, making a stack of four phyllo sheets. Repeat with remaining phyllo and additional cooking spray to make a second stack.
Cut each stack in half lengthwise; cut crosswise into thirds. Press rectangles into prepared muffin cups, pleating as necessary to fit. Bake 5 minutes or just until phyllo starts to brown.
Meanwhile, in a large bowl combine boiling water and couscous; cover and let stand 5 minutes. Fluff with a fork. Stir in the next six ingredients (through salad dressing).
Spoon chicken mixture into partially baked phyllo cups. Bake 5 to 7 minutes more or until heated through and phyllo is golden. Cool in muffin cups on a wire rack 5 minutes. Remove from muffin cups. Serve with Tzatziki Sauce. If desired, serve with lemon wedges.
In a medium bowl stir together yogurt, cucumber, mint, and salt.