Bring a large pot of salted water to a boil and cook fettuccine until al dente according to package specifications.
Reserve 1/2 cup of pasta cooking water, then drain the pasta.
Season chicken cubes uniformly with salt and black pepper.
Heat olive oil in a large skillet over medium-high heat; sear chicken for 6 to 8 minutes or until internal temperature reaches 165 degrees Fahrenheit.
Remove chicken from the skillet and set aside.
Reduce heat to medium, add butter and minced garlic to the skillet, and sauté for 60 seconds until fragrant.
Whisk in heavy cream and lemon zest, bringing the mixture to a gentle simmer for 3 minutes to reduce slightly.
Gradually whisk in parmesan cheese until the sauce is emulsified and smooth.
Incorporate the cooked pasta, seared chicken, and lemon juice into the sauce.
Toss the mixture thoroughly, adding reserved pasta water as needed to achieve desired sauce viscosity.
Garnish with fresh parsley and serve immediately.