If you haven't already, press the liquid out of the tofu either using a tofu press, or by placing a clean towel on top and gently pressing out as much moisture as you can.
Next, slice the tofu into 1" cubes, then place them into a plastic bag. Add 1 tablespoon of soy sauce and 2 tablespoons of cornstarch to the bag, seal it shut and shake it until the tofu is coated.
Heat the olive oil in a large, nonstick skillet over medium-high heat, then add the tofu and cook it until it's nice and crispy on all sides, about 8 minutes. If it seems like it's browning too quickly, reduce the heat to medium.
While the tofu is cooking, make the sauce: whisk the butter, soy sauce, sriracha, lime juice, and cornstarch together in a small bowl.
Once the tofu is cooked, remove the skillet from the heat, then pour in the sauce, stirring until the tofu is coated. It will thicken very quickly, so this shouldn't take long.
Sprinkle with green onions and enjoy!