Heat a large skillet over medium. Add 2 tablespoons olive oil and let it shimmer.

Pat the chicken dry and season both sides with salt and pepper.

Add the chicken to the hot skillet. Don’t move it for 5 to 7 minutes so a deep golden crust forms.

Flip and cook another 5 to 7 minutes until the internal temperature reaches 165°F. Transfer the chicken to a plate and tent with foil to rest.

In the same skillet, add the sliced mushrooms and onions. Sauté, stirring occasionally, until the onions are translucent and the mushrooms have given up moisture and turned golden, about 6 to 8 minutes.

Pour in 1/2 cup heavy cream and stir to combine with the pan fond. Let the sauce simmer 2 to 3 minutes until it thickens slightly and becomes glossy.

Taste and adjust seasoning with salt and pepper.

Nestle the chicken back into the skillet. Spoon the mushroom and onion mixture evenly over each breast.

Sprinkle 1 cup shredded Monterey Jack cheese across the tops.

Cover the skillet and cook 2 to 3 minutes more, just until the cheese melts and becomes gooey.

Serve immediately over warm mashed potatoes so the sauce soaks into the mash.