Pat the chicken dry and season both sides with kosher salt and black pepper.
Heat the olive oil in a large skillet over medium-high heat. Sear the chicken for 5 to 7 minutes per side, until golden and cooked through to 165°F. Transfer to a plate.
Reduce the heat to medium. Add the garlic and sun-dried tomatoes; cook for about 30 seconds, then stir in the chicken broth and scrape up browned bits.
Stir in the cream, Parmesan, and Italian seasoning. Simmer gently for 2 to 3 minutes; add the spinach and stir until wilted.
Return the chicken and any juices to the skillet. Spoon the sauce over it, warm for 1 minute, and serve with lemon if desired.