Begin by preparing the chicken: Place the chicken breasts between two sheets of plastic wrap and gently pound them to an even thickness for uniform cooking.
In a shallow dish, mix the flour, garlic powder, onion powder, salt, and pepper together. Dredge each chicken breast in the flour mixture, shaking off any excess.
In a large skillet, heat 2 tablespoons of olive oil over medium-high heat. Once hot, add the chicken breasts and cook for about 5-6 minutes on each side, or until golden brown and cooked through. Remove the chicken from the skillet and set aside on a plate.
In the same skillet, add the remaining olive oil and sliced mushrooms. Sauté the mushrooms for about 4-5 minutes, or until they are browned and tender.
Stir in the chicken broth, balsamic vinegar, and soy sauce to the skillet. Bring the mixture to a simmer and allow it to reduce slightly, about 3-4 minutes.
Add the cooked chicken breasts back to the skillet and allow them to simmer in the sauce for another 2-3 minutes. Finish by stirring in the butter until melted and the sauce thickens slightly.
Remove from heat and garnish with fresh chopped parsley just before serving.