Season both sides of the chicken thighs with salt and garlic powder. In a large pot or Dutch oven, heat the oil over medium-high heat, then add the chicken thighs. Cook for 2-3 minutes on each side, or until nicely browned.
Add the diced onion and cook for 2-3 minutes until fragrant and translucent. Stir in the sun-dried tomatoes, garlic, ¼ teaspoon of salt, and dried herbs. Cook for 1 minute.
Pour in 6 cups of chicken broth and add the head of cauliflower. Increase the temperature to high to bring to a boil, then reduce to a simmer and cover.
Once the cauliflower is tender (about 20 minutes), remove it from the pot and place it in a large blender. Add a few spoons of the soup broth and the additional cup of broth. Blend until smooth.
Remove the chicken from the pot to shred. If using pasta, add it now; it should cook in just a few minutes from the residual heat.
Stir in the cauliflower puree, shredded chicken, spinach, and Parmesan cheese (if using). Taste and adjust salt and seasonings as needed.
