Start by boiling water in a large pot. Add a generous amount of salt to the pot of water. This will help to season the pasta. Cook pasta according to package instructions. Drain.
While water is heating up, in a large skillet, heat butter and olive oil over medium heat. Add onion and saute for 5-6 minutes. Turn up the heat to medium-high and add chicken breast. Saute for 7-8 minutes. Add garlic and saute for 1 minute. Garlic can easily burn so watch it carefully. Season with salt, pepper, and red pepper flakes.
Add chicken broth and heavy cream or half-n-half. Let simmer for 5 minutes. Stir in lemon juice and lemon zest. If you want more lemon flavor, add more lemon zest. Taste sauce and add more salt, if necessary.
Toss cooked pasta with sauce. Top with freshly grated parmesan cheese and fresh basil ribbons.