Cook the Fettuccine: Bring a large pot of salted water to a boil. Add the fettuccine and cook until al dente, about 5–7 minutes. Drain and set aside, reserving about half a cup of the pasta water.

Prepare the Chicken: Season the chicken breasts with salt and black pepper. In a large skillet, heat olive oil over medium heat. Add the chicken and cook for about 5–6 minutes per side until golden brown and cooked through. Remove from the pan and let rest before slicing.

Sauté the Vegetables: In the same skillet, melt butter. Add the chopped onion and sauté for about 2 minutes until translucent. Add minced garlic and cook for another minute until fragrant.

Cook the Mushrooms: Add sliced mushrooms to the pan and cook for 4–5 minutes until they release their moisture and turn golden brown. Season lightly with salt and pepper.

Make the Creamy Sauce: Pour in the cooking cream and stir well to combine. Reduce the heat to low and let it simmer for about 3 minutes until slightly thickened. Stir in the grated Parmesan cheese until melted and smooth.

Combine Everything: Add the cooked fettuccine and sliced chicken to the sauce. Toss gently to coat, adding a splash of reserved pasta water if needed to loosen the sauce.

Garnish and Serve: Sprinkle chopped parsley on top, adjust seasoning if needed, and serve hot.