Return pan to medium-high heat. Add remaining 2 teaspoons oil to the pan; swirl. Add potatoes, mushrooms, and 1 tablespoon thyme. Cook 3 minutes or until browned stirring once. Combine milk and flour in a bowl, stirring with a whisk. Add flour mixture, stock, lemon, beans, remaining 1/2 teaspoon salt, and remaining 1/4 teaspoon pepper to pan; simmer 1 minute or until slightly thickened. Add chicken; cover, reduce heat and simmer 3 minutes or until beans are crisp-tender. Sprinkle with parsley and serve.