Cook the pasta according to the package directions until al dente. Reserve ½ cup of pasta water before draining.
Heat 1 tablespoon olive oil and butter in a large skillet over medium-high heat.
Season the chicken with salt and pepper. Cook for about 2 minutes per side until golden and fully cooked. Remove and set aside.
Add the remaining olive oil to the skillet. Cook the onion for 2–3 minutes until softened.
Add the mushrooms and cook for another 2–3 minutes until tender.
Stir in the chicken broth, white grape juice, and lemon juice. Simmer until reduced by about half.
Add the chicken stock and heavy cream.
Mix the cornstarch and water until smooth, then stir into the sauce. Bring to a gentle boil and simmer for 2–3 minutes until thickened.
Return the chicken to the skillet and cook for another 30 seconds.
Add the cooked pasta and toss everything together. Add reserved pasta water if needed for a silky sauce.
Stir in parsley and adjust seasoning with salt and pepper.
Serve the Chicken Mushroom Pasta immediately with grated Parmesan if desired