If you haven't already, drain and press the tofu for 10 to 15 minutes. Cut it into bite-size cubes.
Preheat oven to 400°F. Line a rimmed baking sheet with parchment paper and set aside.
Whisk together the tamari, rice vinegar, maple syrup, sesame oil, garlic, and ginger in a container or zip-top plastic bag. Add the cubed tofu to the marinade and toss to coat. Let the tofu marinade for 15 to 20 minutes, stirring every 5 minutes or so to ensure all the tofu gets coated.
After marinating, remove the tofu cubes the marinade (but SAVE the remaining marinade!) and place them spaced out evenly in one layer onto the prepared parchment-lined baking sheet. Bake for 25 to 30 minutes, flipping the pieces over halfway through baking, until golden brown.
While the tofu is baking, whisk the cornstarch into the water until completely dissolved and set aside.
When the tofu is done, set it aside briefly and pour the remaining marinade into a non-stick skillet on the stove over medium-high heat. Add the cornstarch slurry and bring the mixture to a boil. Reduce the heat to a simmer and cook, stirring frequently, until the sauce thickens and resembles a glaze. This should happen quickly. Don't walk away or the sauce could burn or get too thick.
Add the tofu to the thickened sauce and stir to coat thoroughly.
Serve garnished with sliced green onions and sesame seeds.