Pound chicken breasts to even thickness
Season chicken with salt and pepper
Heat olive oil in a skillet over medium-high heat
Add chicken and cook for 6–7 minutes per side until golden and fully cooked
Remove chicken and set aside
Add garlic to the skillet and sauté briefly until fragrant
Add spinach to the skillet and cook until wilted
Stir in lemon juice and zest
Return chicken to the skillet and toss with spinach and garlic
Season with additional salt, pepper, and red pepper flakes
Serve warm