Pat chicken breasts dry and season both sides generously with Cajun seasoning, salt, and pepper.
Heat olive oil in a large skillet over medium-high heat. Add chicken breasts and cook for 5–6 minutes per side, or until golden brown and cooked through. Remove chicken and set aside.
Reduce heat to medium. In the same skillet, add butter and minced garlic. Sauté for 1–2 minutes until fragrant but not browned.
Stir in lemon juice, lemon zest, and chicken broth (or wine), scraping up any browned bits from the bottom of the pan. Simmer for 2–3 minutes to reduce slightly.
Place the seared chicken back into the skillet, spooning the sauce over the top. Simmer for another 2–3 minutes to heat through and absorb flavor.
Sprinkle with chopped parsley and serve with lemon slices, if desired. Spoon extra sauce over each serving for maximum flavor.