Chicken: Season chicken breasts with salt and pepper on a large plate and set aside. Next in a large skillet, add 1 tablespoon of olive oil and 1 tablespoon butter. Allow for butter to melt over medium high heat. When the pan is hot, add chicken and cook for about 4 minutes on each side until browned for a total of 8 minutes. Remove it onto a plate .
Now add the sliced mushrooms and remaining tablespoon of olive oil and 1 tablespoon butter to the pan. Cook for 5 minutes, your mushrooms should look nice and moist, and dark. Once cooked, remove them from the pan.
Sauce: To make the sauce, add remaining butter to the pan, allow it to melt and then cook garlic in it until slightly browned – only for a couple of minutes. Add 1 tablespoon flour and cook until it's no longer raw. Slowly add chicken broth, heavy cream. Once simmering add Parmesan cheese and allow it to blend for 2-3 minutes. Add salt, garlic powder and pepper. Taste the sauce and adjust the seasoning, if necessary.
Add spinach to the sauce and allow it to wilt.
Next cooked mushrooms back into the pan and mix them into the sauce.
Now add cooked chicken and allow it to reheat for 2-3 minutes. Close the lid to help the heat stay in. Serve immediately! Spoon sauce all over chicken.