Preheat a grill or grill pan to medium-high heat.
Brush the chicken breasts with the olive oil and season both sides with the salt and black pepper.
Grill the chicken 5 to 7 minutes on the first side, then flip and grill 3 to 4 minutes more, or until cooked through and the internal temperature reaches 165°F (74°C).
Remove the chicken from the grill and let it rest a few minutes, then slice it for serving.
Meanwhile, cook the fettuccine (or chosen pasta) in a pot of salted boiling water according to package directions; drain and set aside.
In a saucepan over medium-high heat, warm the heavy cream and butter until small bubbles form at the edges; do not boil.
Whisk in the grated Parmesan until smooth and the sauce begins to thicken, about 1–2 minutes.
Stir in the garlic powder if using, taste and adjust seasoning with salt and pepper as needed.
Divide the cooked pasta between plates, spoon the Alfredo sauce over the pasta, and top with the sliced grilled chicken.