Preheat oven broiler.
In a large zipper-topped plastic bag, combine first 4 ingredients (garlic powder through black pepper); shake to combine. Add chicken, one piece at a time, and shake to coat.
Place chicken on an oiled broiler pan and broil 6 inches from heat source for 6 to 8 minutes per side or until juices run clear.
Meanwhile, in a large bowl, toss together spinach, tomato, red onion, cucumber, Herbes de Provence, olives (if using) and cheese; divide mixture equally on 4 chilled salad plates.
Cut the broiled chicken into strips and arrange on top of salads; serve immediately with wedges of lemon.