Prepare the rice according to package directions. I estimated about 40 minutes of cook time for brown rice. You can make the ume tofu bites (see recipe below) at the same time, and complete the remaining steps in the cooking time listed. If so, preheat the oven at the same time you put on the rice water to boil, then immediately make the tofu and put it in the oven before continuing with bowl instructions.
While the rice is cooking, chop your veggies as described in the instructions.
Mix tamari, sesame oil, and lemon lemon juice and set aside.
Prepare your mushrooms. Place a large pan over medium-high heat and drizzle with some extra olive oil. Add the mushrooms all at once and cook until browning slightly. You will want to keep the pan hot and sizzling, with liquids from the mushrooms evaporating quickly, so adjust the heat accordingly.
Once the mushrooms are all a bit brown and mostly cooked, add the scallions to the pan, adding extra oil if necessary so they don't stick. After about one minute, or when scallions are starting to look golden in places, turn off the heat and splash a couple of tablespoons the prepared tamari sauce to the pan, scraping up any browned bits. Set aside.
Once the rice is cooked you're ready to assemble the bowls. Only assemble the bowls you will be serving immediately. Place the veggies in little separate piles around the edge of the bowl, with the tofu in the middle. Scoop some of the mushrooms over the tofu, then drizzle with a couple of spoonfuls of the tamari sauce. Sprinkle over nori and sesame seeds if using, and add a dot of wasabi. You are now ready to serve your bowls!
Put the remainder of the veggies together in a airtight container in the fridge, and the leftover rice and tofu into a separate container and refrigerate. Consume within 5 days.