Prepare the sauce: In a medium saucepan, heat the olive oil over medium heat. Add the minced garlic and sauté for 1 minute until fragrant.
Make the sauce: Add the heavy cream and chicken broth. Bring to a gentle simmer, then lower the heat to medium-low and simmer for about 10 minutes, until the sauce thickens slightly (enough to coat the back of a spoon).
Prepare the chicken: While the sauce simmers, place the chicken breasts in the bottom of your slow cooker. Season with Italian seasoning, sea salt, and black pepper. Top with chopped sun-dried tomatoes.
Finish the sauce: Once the sauce has thickened a bit, reduce the heat to low. Gradually stir in the parmesan cheese, a little at a time, until the sauce is smooth and creamy. Taste and adjust seasoning as needed.
Slow cook: Pour the sauce over the chicken, ensuring the chicken is covered with as much sauce as possible. Cook on High for 3-4 hours or on Low for 6-8 hours.
Wilt the spinach: Once cooking time is complete, remove the chicken from the slow cooker and set it aside. Turn the slow cooker to High, add the chopped spinach, and stir for a few minutes until wilted.
Serve: Return the chicken to the slow cooker, spoon the spinach, sun-dried tomatoes, and sauce over the chicken, and serve.