Place the flour on a plate or shallow bowl and dip the chicken into the flour to coat both sides. Shake off excess flour
Heat a large skillet on medium-high heat and heat the olive oil and 2 tablespoons of the butter. Cook the chicken until golden brown on the bottom, flip, reduce the heat to medium and continue to cook until the chicken is cooked through (160°F), approximately 3-4 minutes per side. Don't overcook! Transfer the chicken to a plate and set aside.
Add the garlic (if using) and stir for 30 seconds then pour the chicken broth and 2 tablespoons of the lemon juice into the pan and stir, scraping the bottom of the pan to release any golden bits, add the lemon zest and remaining 2 tablespoons of the butter.
Turn heat to low and add the chicken back to the pan, turning to coat each side until warmed through. The pan sauce will slightly thicken.