Prep the Chicken: Season the chicken breasts with salt, pepper, and dried thyme on both sides.

Heat the Skillet: Heat olive oil in a large skillet over medium-high heat.

Cook the Chicken: Add the chicken breasts to the skillet and cook for 6-7 minutes on each side, or until golden brown and cooked through. Remove the chicken from the skillet and set aside.

Sauté the Onions and Garlic: In the same skillet, add the chopped onion and cook until translucent. Add the minced garlic and cook for another minute.

Cook the Mushrooms: Add the sliced portobello mushrooms to the skillet and cook until they are tender and browned.

Make the Sauce: Pour in the chicken broth and bring to a simmer. Reduce the heat to low and stir in the heavy cream and Parmesan cheese. Cook until the sauce thickens, stirring occasionally.

Combine and Serve: Return the chicken breasts to the skillet, spooning the sauce and mushrooms over the top. Let it simmer for a few minutes to heat through. Garnish with fresh parsley before serving.