Bring a large pot of water to boil and add 3-4 cabbage leaves, cooking them until just tender (2-3 minutes). Remove and place in a bowl of cold water, set aside, and repeat.
Chop the veggies. Heat oil in a skillet and sauté the onion, garlic, ginger, carrot, peppers, and mushroom for 3-4 minutes. Add the tamari and spices, then cook for a further 1-2 minutes.
For each cabbage leaf, spoon in around 1 ½-2 tbsps of filling. Then fold in the sides and the top over the filling and roll it into a neat parcel. Repeat this with the remaining cabbage rolls.
Heat oil in a saucepan, and add the ginger, garlic, tamari, rice vinegar, and maple syrup. Mix water with cornstarch and pour it into the skillet. Add the spices and cook for a few more minutes.