Shred cauliflower using the largest side of a grater; the end product resembles grains of rice. You can simply chop the very tips of the cauliflower florets with a knife, OR use a food processor. We're only using the flowering part, not the stems.
Steam frozen veggies until tender and heated through, just 3-4 minutes.
Heat oil in a wok. Saute onion, celery, green onions, carrot, and garlic in hot oil until just softened, about 5 minutes.
Add riced cauliflower; cook and stir until cauliflower has a tender but firm to the bite, 4 to 5 minutes.
Stir in soy sauce, and your previously frozen veggies into cauliflower mixture and stir-fry until mixture is hot and slightly browned, 3 to 5 minutes.