Prep the chicken. If using thick breasts, slice them into cutlets for even cooking. Pat dry. Season both sides with salt, pepper, and 1 teaspoon of the ranch seasoning. Lightly dredge in flour if you want a slightly thicker sauce later.

Sear for flavor. Heat oil and 1 tablespoon butter in a large skillet over medium-high heat. Add chicken in a single layer. Sear 3–4 minutes per side until golden and just cooked through (165°F). Transfer to a plate and tent with foil.

Sauté aromatics. Lower heat to medium. Add remaining butter. If using onions or mushrooms, add them now with a pinch of salt and cook 3–5 minutes until softened and lightly browned. Stir in garlic and cook 30 seconds until fragrant.

Deglaze and build the sauce. Pour in chicken broth and scrape up browned bits. Whisk in remaining ranch seasoning and Dijon. Simmer 2–3 minutes to reduce slightly.

Make it creamy. Reduce heat to low. Stir in heavy cream and Parmesan. If using cream cheese, whisk in small pieces until smooth. Simmer gently 2–3 minutes to thicken. Add lemon juice to brighten. Taste and adjust salt and pepper.

Finish the dish. Return chicken and any juices to the pan, turning to coat. If adding spinach or bacon, fold them in now. Simmer 1–2 minutes until warmed through and sauce clings to the chicken.

Garnish and serve. Sprinkle with parsley or chives. Serve over mashed potatoes, rice, pasta, or with roasted green beans and a side salad.