Measure stock into a medium pot and warm over medium heat.
Prepare onion, mushroom, squash, zucchini and carrot.* Set aside.
In a large skillet, melt 1 tablespoon of butter with the oil. When the butter begins to bubble, add onion and stir to combine. Add mushroom and cook until onions are soft and translucent, about 5 minutes.
Add all the rice at once and stir thoroughly, completely coating each grain in butter and giving them a chance to be toasted, about 1 minute.
Ladle 1-2 cups of chicken stock into the hot rice and stir well. Keep heat on medium and continue to cook, adding stock slowly when the previous stock is absorbed, and stirring thoroughly after each addition. Cook for 15 minutes, stirring every few minutes or so. If you need more liquid, add hot water or chicken stock if available.
When the grains are just tender, but not completely done, add the remaining vegetables. Stir to combine and cook for about 5 minutes.
Add the creamy cauliflower sauce, Parmesan, pepper and remaining butter. Stir to just combine. Do not overstir.