Prep the chicken. Pat chicken dry, then season both sides generously with salt, pepper, and a pinch of Italian seasoning.
If the breasts are thick, slice them horizontally so they cook evenly.
Brown the chicken. Heat olive oil and a small knob of butter in a large skillet over medium-high. Sear chicken 4–5 minutes per side until golden and almost cooked through. Transfer to a plate and tent with foil.
Sauté the aromatics. Lower heat to medium.
In the same skillet, add a little more oil if needed. Sauté minced garlic for 30–45 seconds until fragrant. Stir in sliced sun-dried tomatoes and cook 1 minute to wake up their flavor.
Build the sauce. Pour in chicken broth and scrape up any browned bits.
Let it simmer for 1–2 minutes. Stir in heavy cream and a pinch of red pepper flakes. Simmer gently (don’t boil hard) for 2–3 minutes to thicken slightly.
Add Parmesan and greens. Sprinkle in grated Parmesan and stir until smooth.
Toss in the spinach and let it wilt. Taste and adjust salt and pepper. If you like a brighter finish, add a small squeeze of lemon.
Finish the chicken. Return the chicken and any juices to the pan, nestling pieces into the sauce.
Simmer on low for 3–5 minutes until the chicken is cooked through and the sauce is silky and clings to the meat.
Serve. Spoon sauce over the chicken and garnish with extra Parmesan or cracked black pepper. Pair with low-carb sides like zucchini noodles, sautéed broccolini, or cauliflower mash.