For Mushroom Sauce, melt butter in medium saucepan over medium heat.
Add mushrooms; cook until tender.
Remove with slotted spoon; set aside.
Stir flour into pan; cook until bubbly.
Slowly whisk in broth.
Add mushrooms, chives, parsley, mustard, salt and pepper.
Cook, stirring constantly, until thickened.
Stir in sour cream; heat until hot.
Do not boil.
Keep warm on very low heat.
For Chicken, heat oil in large skillet over medium heat.
Add chicken; cook, turning occasionally, about 8 minutes or until chicken is browned and no longer pink in center.
Reduce heat to low; place ham, then cheese on chicken.
Cover and cook 1 to 2 minutes or just until cheese melts.
Place chicken on English muffins.
Spoon sauce over chicken and top with pepper strips.