Step 1: Build the Aromatic Base
In your slow cooker, combine the diced onion, minced garlic, chicken broth, Italian seasoning, onion powder, paprika, salt, black pepper, and red pepper flakes (if using). Stir to combine. Place the raw chicken thighs into the liquid, turning to coat.

Step 2: The Long, Slow Cook
Cover and cook on LOW for 6-7 hours or on HIGH for 3-4 hours. The chicken is done when it is fall-apart tender and easily shreds with a fork. The low and slow method on LOW is highly recommended for the most tender, flavorful chicken.

Step 3: Shred the Chicken
Using two forks, carefully shred the chicken directly in the slow cooker into bite-sized pieces.

Step 4: Thicken the Sauce (Optional)
If you prefer a thicker sauce (highly recommended), create a slurry. In a small bowl, whisk the flour or cornstarch with the ¼ cup of cold water until completely smooth. Stir this slurry into the slow cooker. Cover and cook on HIGH for 20-30 minutes, until the sauce has thickened noticeably.

Step 5: Create the Creamy Sauce
Reduce the slow cooker to the WARM setting (or turn it off). Add the cubed, softened cream cheese and the grated Parmesan cheese. Stir until the cheeses are completely melted and the sauce is smooth.

Step 6: Wilt the Spinach and Enrich
Add the fresh baby spinach to the slow cooker. Gently stir until the spinach is wilted by the heat of the sauce, which will take just 1-2 minutes. If using, stir in the heavy cream or half-and-half for extra richness.

Step 7: Final Seasoning and Rest
Taste the sauce and adjust seasoning with additional salt and pepper if needed. Let the dish sit, covered, for 5-10 minutes to allow the flavors to fully marry and the sauce to reach its perfect, creamy consistency.

Step 8: Garnish and Serve
Serve the creamy spinach chicken over your chosen base—buttered egg noodles, fluffy rice, creamy mashed potatoes, or cauliflower rice for a low-carb option. Garnish generously with fresh chopped parsley or chives and an extra sprinkle of Parmesan cheese.