Drain the block of tofu, then cut into ¾-inch cubes. Dry the cubes with a paper towel. Roll the tofu cubes in the flour, making sure to coat them on all sides.
Heat the oil in a cast iron or non-stick pan until shimmering. Fry the tofu cubes in a single layer until golden brown on all sides (a few minutes on each side). Set aside on a plate lined with a paper towel.
Add all sauce ingredients to a liquid measuring cup. Whisk well until fully combined.
Pour the mix into a saucepan. Bring to a full boil, whisking continuously. Keep boiling the sauce until it becomes translucent and thickens (a few minutes). Take off the heat.
Serve the tofu with rice, drizzle with the sauce and sprinkle chopped scallions on top.