Prep chicken: Pound the chicken breasts to an even thickness. Season both sides with salt and pepper.
Sear chicken: Heat olive oil in a large pan over medium-high heat. Sear chicken for 3-4 minutes per side until golden brown. Remove and set aside.
Make sauce: In the same pan, sauté garlic for 1 minute. Add chicken broth, lemon juice, and zest, scraping browned bits from the pan. Simmer for 2 minutes.
Add cream & cheese: Stir in heavy cream and Parmesan cheese. Simmer until sauce thickens slightly.
Wilt spinach: Add fresh spinach and cook until wilted, about 1 minute.
Combine & cook: Return chicken to pan, spoon sauce over, cover, and cook on low 8-10 minutes until chicken reaches 165°F internally.
Serve: Garnish with parsley and lemon slices. Serve hot.