Prep the Chicken: Pound chicken breasts to an even ½ inch thickness. Season both sides generously with salt and pepper.
Cook the Chicken: Heat olive oil in a large sauté pan. Cook the chicken for 3-4 minutes per side until golden brown and the internal temperature reaches 165°F. Set aside.
Make the Sauce: In the same pan, sauté garlic for 1 minute. Add chicken broth, lemon juice, and zest. Scrape up any bits stuck to the pan. Simmer for a minute, then stir in heavy cream and let it thicken for 5 minutes. Add Parmesan and stir until smooth.
Add Spinach: Stir in the spinach leaves and cook until wilted. Return the chicken to the pan and spoon the sauce over the chicken. Simmer for 2 more minutes.
Serve and Garnish: Garnish with thin lemon slices and extra Parmesan. Serve with pasta, rice, or a low-carb option like cauliflower mash.