Bring a large pot of salted water to a rolling boil. Add the fettuccine and cook according to package directions until al dente. Reserve 1 cup of pasta water, then drain the pasta.

While pasta cooks, pat chicken dry, cut into 1-inch cubes, and season with salt, pepper, and garlic powder. Heat olive oil and 1 tbsp of butter in a large skillet over medium-high heat. Add chicken and cook for 5-7 minutes until golden and cooked through. Remove chicken and set aside.

Reduce heat to medium-low. Add the remaining 4 tbsp of butter to the skillet. Once melted, add minced garlic and cook for 30 seconds until fragrant.

Slowly pour in the heavy cream, whisking constantly. Bring to a gentle simmer and cook for 2-3 minutes to thicken slightly.

Remove skillet from heat. Gradually whisk in the grated Parmesan cheese until the sauce is smooth. Season with salt and pepper. Add a splash of pasta water if too thick. Return cooked chicken and pasta to the skillet, toss to coat, and garnish with fresh parsley before serving.