Heat olive oil in a large skillet over medium heat.
Season chicken breasts with salt and pepper, then sear for 4-5 minutes per side until golden brown and cooked through. Remove from the skillet.
In the same skillet, melt butter and sauté garlic until fragrant.
Add sliced mushrooms and cook until tender, about 5 minutes.
Pour in chicken broth and bring to a simmer, scraping up any brown bits from the pan.
Stir in heavy cream and cook for 3-4 minutes, until the sauce thickens slightly.
Return the chicken to the skillet and coat with the sauce. Let it simmer for 2-3 minutes.
Garnish with parsley and Parmesan, if desired. Serve immediately.