Slice the tofu lengthwise into 4 thin slabs. Arrange in the baking dish in a single layer.
Whisk together everything but the onions. Pour over the tofu and move it around to coat well, then flip and repeat.
Let marinate for at least an hour.
Preheat oven to 375. Pour about half of the marinade back into the bowl and set aside.
Bake tofu for 15 minutes, then baste with some of the reserved marinade, flip, and repeat.
Bake another 10-15 minutes until golden brown and very firm.
Transfer to plates, drizzle with marinade, garnish, and serve hot.