1. Spray a large nonstick skillet with nonstick spray and place over high heat. Sprinkle the chicken with the pepper and 1/4 teaspoon of the salt; cook until browned and cooked through, about 2 minutes on each side. Transfer to a plate and keep warm.
2. Return the skillet to medium-high heat; add the butter and melt. Add the mushrooms, garlic, and remaining 1/4 teaspoon salt; cook, stirring, until the mushrooms brown, about 3 minutes. Add the wine and thyme; simmer until most of the liquid has evaporated, about 4 minutes. Spoon the mushrooms over the chicken and sprinkle with the parsley.