Drain tofu: Drain tofu from its packaging, then let it stand for 5-10 minutes to release extra liquid.
Mix sauce: Mix all the sauce ingredients together in a medium bowl and set aside.
Mix slurry: Mix starch and water together in a small bowl and set aside.
Coat tofu: Drain tofu and cut into slices. Pat dry with kitchen towels and place the slices on a large plate or baking sheet. Sift 1 tbsp of potato starch over the tofu slices and sprinkle with salt and pepper. Flip the tofu and sift the another tbsp of potato starch over. Sprinkle with another pinch of salt and pepper.
Pan fry tofu: Heat oil in a pan over medium high heat. Add tofu (try to keep some space between the slices or they will stick) and cook until brown on the bottom, 3-5 minutes. Flip and brown the other side, another 3-5 minutes. Transfer tofu to a plate.
Cook veggies: Add the veggies to the pan and cook until mushrooms just start to soften, 1-2 minutes.
Add sauce: Turn heat down to medium and pour in the sauce. Simmer about 3 minutes or until veggies are just tender.
Add slurry: Give the slurry a quick mix then drizzle into the pan, stirring constantly. Remove from heat once the sauce thickens (it should thicken quickly after adding the slurry).
Pour over tofu: Pour the sauce over the tofu and serve immediately.
Notes
1) Tofu: Silken/soft tofu can be used instead. Skip the pan frying step and instead heat the tofu in the microwave for 1-2 minutes, or simmer in water/broth on the stove until warm. Then make the sauce as directed and pour over the tofu.2) Kombu Dashi: Soak 3g of dried kombu in 200ml water at room temperature for 2-3 hours. Or use instant kombu dashi powder* (1/2 tsp dissolved in 200ml water).3) Coconut Aminos + Rice Vinegar: These can be omitted and replaced with 1 tbsp soy sauce + 1 tbsp mirin.