Mix the sauce ingredients together, except for the cornstarch - set that aside for now.
Reserve half of the sauce for a marinade for the tofu, and half for the stir fry.
Slice the tofu. I like to cut the block into 6 sliced, then cut each slice into 4 triangles. You can also cube it.
Place in a container or shallow bowl and pour in half of the teriyaki sauce. Toss gently so each piece of tofu is coated.
Let marinate for 30 minutes (you can also leave it overnight in the fridge.) Toss or flip halfway.
Got some remaining sauce? Add that to the half you reserved.
In a large pan or wok, heat 1 tablespoon of the oil on medium-low heat. Add the tofu to the pan. Cook until browned on each side (a total of about 8 minutes.) Remove tofu from the pan and set aside for now.
Add the remaining tablespoon of oil to the pan. Cook the sliced onion until translucent.
Add in mushrooms and carrots. Cook until carrots are tender.
Add broccoli, bell peppers, snap peas, and 2 tablespoons of water to the pan. Cook, covered, until just tender. Add more water if necessary.
Whisk the cornstarch into the reserved teriyaki sauce. Add the tofu back into the pan along with the teriyaki sauce. Toss. Cook for another 2 minutes, or until the sauce has thickened and the tofu is warm again.
Serve with rice for a satisfying meal. Optional: Garnish with sesame seeds and sliced green onion.