Season the chicken: Pat the chicken dry.
Sprinkle with salt, pepper, and Italian seasoning on both sides. This builds flavor from the start.
Layer the base: In your slow cooker or a 9x13-inch baking dish, add the chicken broth, sun-dried tomatoes, garlic, and oil. Stir to combine.
Place the chicken in a single layer on top.
Add the creamy elements: Scatter the cream cheese cubes around the chicken. Pour in the heavy cream and sprinkle with Parmesan. If you like heat, add red pepper flakes.
Cook it low and slow: For slow cooker: cook on Low for 4–5 hours or on High for 2–3 hours, until the chicken is tender and 165°F in the thickest part.
For oven: cover with foil and bake at 375°F (190°C) for 30–40 minutes, depending on thickness.
Stir in the greens: When the chicken is done, add the spinach and stir gently into the sauce. The heat will wilt it in about 2–3 minutes.
Adjust the sauce: If the sauce seems too thick, whisk in a splash of warm broth or cream. If it’s thin, let it sit uncovered for a few minutes or stir in extra Parmesan.
Taste and finish: Taste for salt and pepper and adjust.
Garnish with fresh basil or parsley.
Serve: Spoon over pasta, mashed potatoes, rice, or creamy polenta. Add a squeeze of lemon if you want a little brightness.