Prep the chicken. Slice the chicken breasts into thinner cutlets for faster, even cooking. Pat dry with paper towels. Season both sides with salt, pepper, and Italian seasoning.
Brown the chicken. Heat the olive oil in a large skillet over medium-high heat.
Add the chicken and cook 4–5 minutes per side, until golden and just cooked through. Transfer to a plate and tent with foil.
Add butter and aromatics. Lower heat to medium. Add butter to the same pan.
Stir in the garlic and cook 30 seconds until fragrant. Don’t let it brown.
Build the base. Stir in the sun-dried tomatoes and cook 1 minute. Pour in the chicken broth, scraping up any browned bits from the bottom of the pan.
Simmer 2–3 minutes to reduce slightly.
Make it creamy. Reduce heat to medium-low. Stir in the heavy cream and bring to a gentle simmer. Let it bubble for 2–3 minutes to thicken slightly.
Add cheese and seasoning. Stir in the Parmesan until melted and smooth.
Taste and adjust salt and pepper. Add a pinch of red pepper flakes if you like heat.
Finish with greens. Fold in the spinach and cook until just wilted, about 1 minute. Add lemon juice if using for a fresh lift.
Return the chicken. Nestle the chicken back into the sauce along with any juices.
Spoon sauce over the top and simmer 2 minutes to warm through.
Serve. Garnish with chopped basil or parsley. Serve over pasta, mashed potatoes, rice, or with crusty bread.