Heat butter (or ghee) on medium heat until melted. Add chopped onion, carrots, and celery and cook until onions are translucent, about 7 min. Add garlic and cook 1 more minute, stirring frequently.
Add chicken breasts and cook almost through- about 8 minutes.
Sprinkle the cassava flour and thyme over the chicken mixture and stir until evenly coated. Add the coconut milk and bone broth and bring to a boil.
Add the cauliflower rice and continue to simmer for 5 more minutes, or until the cauliflower rice is soft. Add salt and pepper to taste.