On a large plate, combine flour with 1/4 cup Parmesan, garlic powder, and lemon zest. Season generously with salt and pepper and mix thoroughly with a fork. Dredge each chicken breast on all sides with a flour mixture. Set aside.
In a large skillet over medium-high heat, heat oil until shimmering but not smoking. Add chicken and sear until golden, 6 minutes. Flip and cook until the opposite side is golden, around 6 minutes more. Remove from pan and set aside.
Turn heat down to medium and add butter to the pan. When butter is melted add garlic and cook until fragrant, about 1 minute. Add spinach and cook until wilted, 1 to 2 minutes. Add chicken broth, cream, and remaining 1/2 cup Parmesan and season with more salt and pepper. Stir to combine. Add lemon slices bring to a simmer and cook until thickened slightly 3 to 4 minutes. Return chicken to skillet and simmer until chicken is cooked through, 5 to 6 minutes more.
When chicken is cooked, remove skillet from heat and garnish with basil before serving.
