Bring a large pot of salted water to a boil. Cook the fettuccine according to package directions until al dente. Before draining the pasta, reserve up to 2 cups of the pasta water. Drain the pasta and return it to the pot. Cover to keep warm.

While the pasta cooks, prepare the chicken. In a large bowl, combine the minced garlic, oregano, salt, and pepper. Add the cubed chicken and toss until evenly coated.

Heat a large skillet over medium-high heat. Add the butter and allow it to melt. Add the chicken in a single layer, cooking in batches if necessary to avoid overcrowding. Cook for 3-4 minutes until lightly browned on the bottom, then flip and cook another 3-4 minutes until golden and cooked through (165°F). Remove from heat and allow the chicken to rest while you prepare the sauce.

To make the Alfredo sauce, melt the butter in a medium saucepan over medium heat. Add the cream cheese and garlic powder and whisk until completely smooth. Slowly whisk in the milk and ½ cup of the reserved pasta water until fully incorporated. Stir in the Parmesan cheese and season with salt and pepper. Remove from heat once the sauce is smooth.

Pour the Alfredo sauce over the warm pasta. Add the cooked chicken and toss until evenly coated. If needed, add additional pasta water a little at a time, tossing until the sauce evenly coats the pasta. The sauce will thicken as it cools, so extra pasta water can help loosen it. Serve immediately and garnish with fresh parsley if desired.