Heat avocado oil in a sauté pan over medium heat.
Add the mushrooms and onions, and sauté for about 10 to 15 minutes, until the onions are translucent and browned, and the mushrooms are soft and browned.
The mushrooms should reduce in size by at least half, and no liquid should remain. (If needed, you can increase the heat at the end to help evaporate the liquid.)
Add the minced garlic and thyme. Sauté for about 1 minute, until fragrant.
Add the cauliflower and chicken stock. Increase heat to bring to a simmer, then simmer, stirring occasionally, until the cauliflower is tender, and liquid is reduced, about 3-5 minutes.
Reduce heat to low. Stir in the grated mozzarella. Continue to heat, stirring constantly, for about a minute, until the cheese melts and sauce is smooth.
Season with sea salt and black pepper to taste.
