Cook the fettuccine according to package instructions in a large pot of salted boiling water. Drain and set aside, reserving 1/2 cup of pasta water.
In a large skillet, heat the olive oil over medium heat. Add the chicken pieces, season with salt and pepper, and cook until golden brown and cooked through, about 5-7 minutes. Remove the chicken from the skillet and set aside.
In the same skillet, add the minced garlic and sauté for about 1 minute until fragrant.
Pour in the heavy cream, stirring to combine, and bring to a gentle simmer.
Add the grated Parmesan cheese, Italian seasoning, and red pepper flakes (if using). Stir until the cheese is melted and the sauce is creamy.
Return the cooked chicken to the skillet and add the drained pasta. Toss everything together, adding reserved pasta water as needed to reach desired sauce consistency.
Serve immediately, garnished with fresh parsley.