In a skillet, melt the butter over medium heat. Add the green onions and mushrooms and cook for 10 minutes.
Add the cauliflower rice, stir and cook for 5 minutes.
Transfer the cauliflower rice mixture to a 4- to 6-quart slow cooker. Add the vegetable broth, sea salt, and black pepper. Cover and cook on LOW for 4 hours or until thick and creamy.