| 3 tbsp | Balsamic vinegar |
| 1 tsp | Olive oil |
| 1 tsp | Rosemary |
| 3 | Garlic cloves |
| 1/4 tsp | Salt |
| 1/8 tsp | Black pepper |
| 1 | Medium onion, sliced into 1/2-in thick slices |
| 2 | Chicken breasts |
| 2 | Whole wheat pita pocket bread rounds |
| 2 | Plum tomatoes, sliced |
| 1 cup | Packed fresh baby spinach leaves |
| 4 slices | Reduced fat cheese |
Combine vinegar, oil, rosemary, garlic, salt, and pepper. Set aside 2 tbsp of vinegar mixture. Pound chicken flat and then cut each breast in half. Brush onion and chicken with remaining vinegar mixture.
Heat grill or grill pan over medium-high heat. Lightly coat pan with oil. Place pita bread rounds in pan; grill 1-2 minutes on each side. Remove from pan. Place onion and chicken in pan; cook onions 4-6 minutes until grill marks are visible and chicken until no longer pink.
Slice tomatoes. To assemble sandwiches, cut pita rounds in half. Line each pita round with spinach leaves, one slice cheese, one slice onion, one piece of chicken and tomato slices. Drizzle each pita with reserved vinegar mixture. Serve immediately.