Heat a medium or large pot over medium high heat.
Once hot, add the oil. Stir-fry the onion, white part of green onion, and ginger until aromatic - around 1 minute.
Add the garlic and stir-fry for 30 seconds. Add the bell pepper. Stir-fry for 1 minute.
Add the sliced mushrooms then season with a pinch of salt and freshly ground pepper to taste.
Stir-fry the mushrooms for 1-2 minutes.
Mix the sauce again since the corn starch tends to settle at the bottom of the bowl.
Over medium heat, pour the sauce into the mushroom mixture.
Mix well and allow the sauce to come to a boil. It will start to thicken from the starch.
Add the silken tofu into the pot.
Carefully mix the tofu into the sauce. Don’t over mix since this can easily break apart the silken tofu.
Add more of the mushroom water if you want to thin out the sauce. I added 1-2 tbsp water since I wanted my sauce thick to serve over rice. You can add more or less depending on your preference.
Taste the tofu with the sauce. Feel free to season with more soy sauce, to taste, if needed.
Finish the tofu with sesame oil, chili oil (if desired), and chopped green onions.
Serve while hot and enjoy over or with rice.