Bring a large pot of salted water to a boil for the pasta.
Season the chicken pieces with some of the black pepper and salt.
In a large skillet, heat the oil over medium-high heat. Add the seasoned chicken and cook for 5-6 minutes per side until lightly browned. Remove chicken from skillet and set aside.
In the same skillet, melt the butter. Add the minced garlic and cook for 1 minute until fragrant.
Pour in the chicken broth and lemon juice. Add the rest of the black pepper and salt. Let it simmer for 2-3 minutes, scraping up any browned bits from the bottom of the pan.
Stir in the heavy cream and bring to a gentle simmer. Let simmer for 5 minutes to thicken slightly.
Meanwhile, cook the tagliatelle in the boiling salted water according to package instructions until al dente.
Add the cooked chicken and any juices back into the cream sauce. Allow to simmer for 2-3 minutes.
Turn down the heat and stir in the Parmesan cheese until melted and combined. Taste the sauce and adjust for seasoning accordingly.
Drain the cooked tagliatelle and add it directly to the creamy chicken sauce. Toss to coat the noodles evenly.
Serve the creamy chicken tagliatelle immediately, garnished with extra Parmesan and parsley if desired. Enjoy!