First mix the liquid ingredients together for the sauce in a glass measuring beaker that holds at least 2 cups of liquid. Add the minced garlic and enough water to bring the measure up to 2 cups. Mix the tablespoon of arrowroot with a little of the sauce liquid in a separate bowl or cup then add it back into the sauce mixture stirring well. Set aside.
Stir fry the tofu in a little oil. Try to get a bit of brown on the cubes and leave the scrapings in the pan. Take the tofu cubes from the frying pan and reserve them for later.
Stir fry the broccoli stems for about 7 minutes (add the leeks and mushrooms if you're using them) then add the florets, cook for another 5 minutes and add the tofu back to the pan. Pour on the sauce mixture. Bring up to the boil - the sauce will thicken - stir to incorporate everything, then turn off the heat and serve over brown rice.