Directions

1. Gather all ingredients.
2. Preheat the oven to 400 degrees F (200 degrees C).
3. Place a chicken breast between two sheets of plastic wrap and set on a cutting board. Pound with a meat mallet to 1/2-inch thickness. Repeat with remaining chicken.
4. Sprinkle chicken with salt and pepper. Then sprinkle chicken generously with flour, shaking off excess.
5. Heat oil in an ovenproof 12-inch skillet over medium-high heat. Add chicken to the skillet and brown 3 minutes per side (chicken may not be fully cooked). Transfer chicken from the skillet to a plate.
6. Reduce heat to medium. Add onion to the skillet; cook and stir until tender, 4 minutes. Add garlic; cook and stir until fragrant, 1 minute more.
7. Add broth, cream, lemon zest and juice, rosemary, and crushed red pepper. Bring to a boil, about 2 minutes.
8. Add spinach, in batches, stirring until wilted, about 1 minute.
9. Stir in 1/4 cup Parmesan cheese and simmer until desired consistency, about 5 minutes.
10. Return chicken to skillet. Sprinkle with remaining 1/4 cup Parmesan cheese.
11. Bake in the preheated oven until chicken is cooked through and sauce is bubbling, 10 to 15 minutes. An instant read thermometer, inserted into the thickest part of chicken, should read 165 degrees F (74 degrees C).
12. Serve garnished with lemon slices.