Prep the chicken: Pat the chicken dry. Season both sides with 3/4 teaspoon salt, pepper, garlic powder, and paprika.
Sear for flavor: Heat olive oil in a large skillet over medium-high heat.
Add chicken and cook 3–4 minutes per side until golden and nearly cooked through. Transfer to a plate; tent loosely with foil.
Sauté the garlic: Reduce heat to medium. If the pan looks dry, add a small knob of butter.
Add minced garlic and cook 30 seconds until fragrant. Don’t let it brown.
Deglaze: Pour in chicken broth and scrape up browned bits. Let it simmer 2–3 minutes to reduce slightly.
Make it creamy: Stir in heavy cream and Dijon.
Bring to a gentle simmer. Keep the heat medium-low to prevent curdling.
Add Parmesan: Sprinkle in Parmesan gradually, stirring until melted and smooth. If too thick, add a splash more broth; if too thin, simmer another minute.
Brighten the sauce: Stir in lemon juice (and zest if using).
Taste and add the remaining 1/4 teaspoon salt if needed.
Add greens: Stir in spinach until wilted, about 1 minute.
Finish the chicken: Return chicken and any juices to the skillet. Spoon sauce over the top and simmer 2–3 minutes until the chicken is cooked through (internal temp 165°F/74°C).
Garnish and serve: Sprinkle with fresh parsley or basil and extra Parmesan. Serve hot with your favorite low-carb sides.