Prep the slow cooker: Lightly grease the insert with the reserved sun-dried tomato oil.
This adds flavor and helps prevent sticking.
Season the chicken: Pat the chicken dry and season both sides with salt, pepper, Italian seasoning, and smoked paprika. Lay the pieces in a single layer in the slow cooker.
Add the flavor base: Scatter the sliced sun-dried tomatoes and minced garlic over the chicken. These will perfume the sauce as it cooks.
Make the creamy sauce: In a bowl, whisk together the heavy cream, cream cheese cubes, and 1/2 cup Parmesan.
Don’t worry if the cream cheese doesn’t fully dissolve; it will melt in the slow cooker.
Pour and cook: Pour the cream mixture over the chicken. Cover and cook on Low for 3.5 to 4.5 hours (thighs) or 2.5 to 3.5 hours (breasts), until the chicken is tender and reaches 165°F.
Finish the sauce: If using, stir in the red pepper flakes. For extra body, remove the lid for the last 15–20 minutes to gently thicken.
Alternatively, mash a few sun-dried tomatoes into the sauce to boost texture and flavor.
Optional greens: Stir in the spinach during the last 5 minutes. It will wilt quickly without watering down the sauce.
Taste and garnish: Adjust salt and pepper as needed. Top with extra Parmesan and chopped basil or parsley before serving.