Halve the tofu lengthwise and place it between two layers of kitchen paper or a clean dish towel. Press firmly on the tofu block to squeeze out as much liquid as possible. Then cut the tofu into 0.5-centimeter-thick slices and cut these slices into approximately 2- to 3-centimeter cubes, resulting in thin rectangles.

Place cornstarch in a bowl or deep plate and carefully roll the tofu slices in it using a dough scraper, ensuring they are evenly coated on both sides.

Heat oil in a large, non-stick frying pan and spread it evenly. Place the tofu pieces side by side in the pan and fry over medium-high heat for about 5 minutes, until the underside is golden brown and crispy.

Meanwhile, mix soy sauce, rice vinegar, sriracha, and ketchup in a bowl. Slice the spring onions into thin rings.

Once the tofu is golden brown and crispy on the bottom, flip it and fry for another 3 to 5 minutes on the other side. Once the other side is also golden brown, reduce the heat to low, add the sauce, and stir-fry for 30 to 60 seconds until the sauce has thickened slightly, has a sticky consistency, and all the tofu pieces are evenly coated. Serve the tofu with the spring onions and your choice of side dishes.