Place a large skillet over medium heat and add in the oil. Once oil heats, add in the onions and cook for 5-7 minutes or until onions soften.
Add in the celery, garlic, water, pepper and bring to a boil. Once boiling, reduce heat and let simmer for 1 minute. Then, strain the vegetables from the broth and add in the mushrooms and carrot noodles.
Bring the heat up to a rapid simmer and let cook for 2-3 more minutes or until carrot noodles are cooked to your preference. Stir in the scallions and let simmer for 1 more minute and then divide into bowls and serve.