Mix the ingredients of the marinade together, add the chicken and let it sit in the fridge for 1 hour or more.
In a large oven safe skillet, heat olive oil over medium-high heat. Once the oil is hot, add the seasoned chicken breasts to the skillet. Sear them for 5-6 minutes on each side, or until they develop a golden brown crust. Remove the chicken from the skillet and set it aside momentarily.
In the same skillet, add the sliced mushrooms. Sauté them for 5-6 minutes, or until they become soft and caramelized, releasing their delicious flavors. Set aside.
In the same skillet add the onion and cook until they are caramelized. Set aside
Once the onions and mushrooms are cooked, return the seared chicken breasts to the skillet, add the onions and mushrooms on top.
Sprinkle the shredded Monterey Jack cheese evenly over the chicken breasts, covering them generously with the ooey-gooey goodness.
Preheat your oven to 375°F. Transfer the skillet to the preheated oven and bake for 15 minutes, or until the cheese is melted and bubbly.
Once the cheese is melted, remove the skillet from the oven and garnish the dish with fresh parsley.