Cook the Pasta: Boil a large pot of salted water, cook fettuccine until al dente, then drain and set aside.
Prepare the Chicken: Slice chicken into strips, season with salt and pepper, then sauté in olive oil until fully cooked. Remove and set aside.
Sauté Vegetables: In the same pan, sauté onions in butter and olive oil, add mushrooms, and cook until softened. Stir in minced garlic for added flavor.
Make Alfredo Sauce: Pour half-and-half into the pan, bring to a light boil, and cook until slightly thickened.
Combine Ingredients: Add the cooked chicken, parsley, salt, and pepper. Stir in drained pasta, mixing well to coat with the sauce.
Rest & Serve: Let the pasta sit for 10 minutes to thicken. Serve with fresh parsley and grated Parmesan cheese.