Bring a pot of water to a boil. Salt the water well, and add pasta. Heat a large skillet over low heat. Add oil, garlic, and crushed red pepper. Cook until the oil sizzles (about 7-10 minutes). Add lemon juice, half-and-half, and a ladle of the pasta water to the garlic oil mixture. Raise the heat to med-low to med heat until the sauce begins to bubble. Drain pasta – DO NOT RINSE. Add the pasta, zest, and 1/2 c. Parmesan to the cream sauce. Toss for a minute or two. Add chicken and spinach, and toss until well distributed. Top with remaining cheese. Enjoy!