Start by marinating the chicken breasts. In a bowl, mix olive oil, garlic powder, salt, and black pepper. Coat the chicken breasts in this mixture and let them sit for at least 30 minutes to absorb the flavors.

While the chicken is marinating, bring a large pot of salted water to a boil. Add the fettuccine and cook according to package instructions until al dente. Drain the pasta, reserving about 1 cup of pasta water, and set aside.

Preheat a grill or grill pan over medium-high heat. Once hot, add the marinated chicken breasts and grill for about 6-7 minutes on each side, or until the internal temperature reaches 165°F (75°C). Remove from the grill and let rest for a few minutes before slicing into strips.

In a large skillet, melt the butter over medium heat. Pour in the heavy cream and bring to a gentle simmer. Stir in the grated Parmesan cheese, mixing until it melts and the sauce thickens slightly. If the sauce is too thick, add a little reserved pasta water to reach your desired consistency.

Add the cooked fettuccine to the skillet and toss to coat the pasta evenly in the creamy sauce. If using, sprinkle in the nutmeg for extra flavor.

Serve the fettuccine Alfredo on plates, topped with the sliced grilled chicken. Garnish with fresh parsley, if desired, and enjoy your delicious meal!