In a small bowl combine oregano, salt, black pepper and garlic powder.
Place chicken on a cutting board and slice them horizontally so you now have 4 chicken breasts pieces. Lay them flat and season on both sides with the seasoning mix.
In a large skillet heat oil on medium high then sear chicken breasts on both sides until golden brown. 2-3 minutes per side.
Remove chicken and set aside.
Reduce heat to medium add butter, onions and garlic saute for 2 minutes.
Add chicken broth and deglaze the pan with a wooden spoon to release all the brown bits at the bottom.
Mix in dijon mustard, Worcestershire sauce, heavy cream and parmesan cheese.
Simmer sauce until cheese melts, taste to adjust seasoning adding more oregano, salt and pepper to taste.
Nestle the chicken breast back in with any accumulating liquids in the plate.
Spoon sauce on top of chicken and allow everything to heat up together for 2-3 more minutes.
Serve with potatoes.