01 - Place chicken breasts between sheets of plastic wrap and gently pound to an even 1/2-inch thickness.
02 - In a shallow bowl, combine flour, salt, and black pepper. Dredge each chicken breast in the seasoned flour mixture, shaking off excess.
03 - Heat olive oil in a large skillet over medium-high heat. Add chicken breasts and cook for 4 to 5 minutes per side until golden brown and cooked through. Transfer to a plate and cover loosely with foil.
04 - In the same skillet, melt butter over medium heat. Add sliced mushrooms and cook, stirring occasionally, until browned and tender, approximately 5 to 6 minutes.
05 - Add minced garlic to the skillet and cook for 1 minute until fragrant.
06 - Pour in chicken broth, grape juice, balsamic vinegar, and thyme. Bring to a simmer while scraping up browned bits from the pan bottom.
07 - Simmer for 5 to 7 minutes until the sauce is slightly reduced. If thicker sauce is desired, stir in cornstarch slurry and cook for 1 to 2 minutes until thickened.
08 - Return chicken to the skillet, spooning sauce and mushrooms over the top. Simmer for 2 to 3 minutes to heat through.
09 - Sprinkle with fresh parsley before serving.