To prepare the mushrooms, wash well and remove stems. Marinate in Balsamic Marinade for 1 hour to overnight.
To prepare the stuffing, chop onion into very small pieces and sauté until golden. Add chopped celery and peppers and
sauté until vegetables begin to soften but are still firm.
Preheat oven to 375°F. Bake Portobello mushrooms for 30 minutes; they will give off liquid and shrink considerably. Allow to cool and spill off liquid.
In the bowl of a food processor fitted with the S blade, process the celery root cubes until consistency resembles rice. Line
a cookie sheet with parchment paper and spray with oil. Lay the celery root rice on the cookie sheet and bake for 20-25 minutes. (Mushrooms and cauliflower may be baked simultaneously.)
Combine the sautéed vegetables with the celery root rice. Add coconut aminos or tamari sauce and salt and pepper to taste.
Stuff mushrooms with vegetable mixture. Top with cheese to taste, if using, and re-bake for 10 minutes to melt the cheese.