Combine all marinade ingredients. Place chicken breasts in marinade and refrigerate for 2 to 4 hours.
Slice peppers and onions and sauté in olive oil until al dente. Season with salt and pepper.
Saute chicken breasts in olive oil over medium heat; cook evenly on both sides to a golden brown color.
Heat cast iron skillet on burner over medium heat until very hot. Place mashed potatoes on top portion of skillet. Place cheeses on bottom portion of skillet and cover with pepper and onion medley. Add chicken to top of pepper and onion medley, resting on potatoes. Top with chopped parsley. Serve “sizzling.".