Season chicken breasts with salt and pepper and place them in a single layer at the bottom of the slow cooker.
In a medium bowl, combine chicken bone broth, minced garlic, red pepper flakes, oregano, and thyme; pour the mixture over the chicken.
Add the chopped sun-dried tomatoes on top of the chicken breasts.
Cover and cook on low for 4 hours (or high for 2 hours) until the internal temperature of the chicken reaches 165 degrees Fahrenheit.
Remove the chicken from the slow cooker and transfer to a plate to rest; shred or slice into bite-sized pieces.
Whisk the Greek yogurt and grated parmesan cheese into the warm liquid remaining in the slow cooker until the sauce is uniform and creamy.
Stir in the fresh baby spinach and return the chicken to the pot, tossing to coat.
Cover the slow cooker for an additional 5 to 10 minutes until the spinach is wilted and the sauce has thickened slightly.