Season chicken breasts with salt and pepper on both sides. Heat olive oil in a large skillet over medium-high heat until shimmering. A drop of water should sizzle on contact when the pan is ready. Add chicken and cook for 5 to 6 minutes per side without moving until deep golden brown. Internal temperature should reach 165 degrees F. Remove from skillet and set aside.

Lower heat to medium-low. Add minced garlic to the same skillet and saute for about 30 seconds until fragrant. Watch carefully as garlic can burn quickly and turn bitter. Pour in the cream, stirring continuously. Add Italian seasoning and Parmesan cheese, stirring until smooth and fully melted. If using spinach, stir it in now and simmer for 2 to 3 minutes. Pull from heat when the sauce is slightly thinner than desired as it will thicken as it cools.

Return the cooked chicken to the skillet. Spoon the creamy garlic Parmesan sauce generously over each piece. Simmer together for 1 to 2 minutes to reheat the chicken and blend the flavors. If the chicken has cooled significantly, extend to 2 to 3 minutes. Remove from heat and serve hot.