Modified from a recipe from www.weightwatchers.com called "Balsamic Chicken with Mushrooms". SERVING SUGGESTION: Serve with cranberry beans and parsleyed potatoes.
In a medium, non-reactive bowl, mix vinegar, mustard and garlic. Add chicken and turn to coat.
Transfer chicken and marinade to skillet. Sauté chicken until cooked through, about 2-3 minutes per side. Transfer chicken to a platter and keep warm.
Add tomatoes to skillet. Sauté mushrooms for 1 minute. Add broth and thyme. Cook, stirring occasionally, until mushrooms are deep brown (about 2 minutes longer).
Serve chicken topped with mushrooms. Sprinkle feta on top and garnish with fresh thyme (if desired).