Preheat oven to 400°. Cut a pocket into each chicken breast and season the inside and the outside of the breast with salt and pepper. Set aside. In a large skillet over high heat cook 1/2 cup of onions with the butter until translucent, about 5 minutes. Add the garlic and the mushrooms, cook until soft and browned about 10 minutes. Remove from heat and pour into a bowl. Stir in the cheese and thyme. Add the breadcrumbs in increments until the mixture is stiff enough to form a loose ball. Stuff the mixture inside the chicken breasts. In the same skillet over high heat sear the chicken breast in the olive oil just until brown. Place on a baking sheet and put them in the oven to finish, about 10 minutes. Meanwhile add the remaining 1/2 cup onions and 1 clove garlic to the pan and cook until soft. De-glaze with wine. Add the chicken stock and cream and season with salt and pepper. Place the chicken breasts on a platter and pour the sauce over. Garnish with parsley.