In a large pot of boiling salted water, cook the fettuccine according to package instructions until al dente. Drain and set aside.
In a large skillet over medium-high heat, add olive oil. Season the chicken pieces with salt and pepper. Add the chicken to the skillet and cook until golden brown and cooked through, about 6-8 minutes. Remove the chicken from the skillet and set aside.
In the same skillet, add a little more olive oil if needed, and then add the chopped onion. Sauté until translucent, about 3-4 minutes. Add the minced garlic and cook until fragrant, about 1 minute.
Pour in the chicken broth, stirring to deglaze the pan. Let it simmer for about 2 minutes, then lower the heat and add the heavy cream. Stir in the Parmesan cheese along with the dried thyme, oregano, and basil. Cook on low heat until the cheese melts and the sauce thickens, about 5-7 minutes.
Add the cooked chicken and spinach into the creamy sauce. Stir well to combine, allowing the spinach to wilt slightly.
In a large mixing bowl or directly in the skillet, add the drained fettuccine to the creamy chicken and herb sauce. Toss until the pasta is well coated. Adjust seasoning with additional salt and pepper if needed.
Divide the creamy herb chicken pasta among plates. Garnish with freshly chopped parsley and extra grated Parmesan if desired.