In a small bowl whisk chicken broth, juice of 1 lemon and 1 tsp mustard. Set aside. 


In a large nonstick skillet heat the olive oil, add the chicken, onion and cook for 6 min.  
Add the garlic, mushrooms, oregano, yellow pepper and cook for 6 min more.
  Add the chicken broth, salt, season with pepper and simmer for 15 min or until chicken is tender.


Remove from heat, top with tomato wedges, sprinkle with fresh parsley and feta cheese (optional) and serve.