Heat a large pot over medium heat. Add the butter to pot, then stir in onions. Cook onions until translucent (about 2-3 minutes).
Add the cauliflower rice, pumpkin puree and salt to the pot and cook for 2-3 minutes.
Add one quarter (4 ounces) of vegetable stock to the pot and bring to a low low boil. Cook for 5 minutes or until the liquid starts to reduce. Stir frequently.
Repeat this process three more times or until all of the liquid has been added to the pot. The final sauce should be creamy.
Turn off the heat and stir in the parmesan cheese.