Season the chicken. Pat the chicken dry with paper towels. Sprinkle both sides with salt, pepper, and Italian seasoning.
This helps build a flavorful crust.
Sear the chicken. Heat olive oil in a large skillet over medium-high. Add the chicken in a single layer and sear 4–5 minutes per side until browned and nearly cooked through. Transfer to a plate; tent loosely with foil.
Sauté aromatics. Lower heat to medium.
If the pan looks dry, add a splash more oil. Add garlic and red pepper flakes. Stir 30 seconds until fragrant, being careful not to burn the garlic.
Build the base. Stir in the sun-dried tomatoes and cook 1 minute.
Pour in chicken broth, scraping up browned bits with a wooden spoon. Simmer 2–3 minutes to reduce slightly.
Make it creamy. Stir in heavy cream and Parmesan. Simmer gently 2–3 minutes until the sauce thickens and coats the spoon.
Add the butter if using for extra gloss.
Add greens. Fold in spinach and let it wilt, about 1 minute. Taste the sauce and adjust salt and pepper if needed. A small squeeze of lemon brightens the dish without adding carbs.
Finish the chicken. Return the chicken and any juices to the pan.
Spoon sauce over the pieces. Simmer on low 3–5 minutes until the chicken is cooked through and the sauce is silky.
Serve. Garnish with chopped basil. Serve with cauliflower rice, zucchini noodles, or a side of roasted asparagus.