Place soy sauce, tomato paste, rice vinegar, sugar, corn flour and sweet chili sauce in a small bowl. Stir to combine. Add a little water if the mixture is too thick. Set aside.
FRY TOFU:
Place tofu cubes in a large bowl. Sprinkle with corn flour. Toss to coat the tofu pieces in flour. Set aside.
Meanwhile, heat oil in a large frying pan over medium-high heat. Add tofu (in batches depending on the size of the pan). Fry until all sides are browned. Remove from pan. Set aside.
SWEET AND SOUR TOFU:
Wipe the pan clean. Add oil. Once hot, add ginger and garlic. Sauté, stirring, for a minute or until fragrant.
Add scallions or spring onions. Sauté, stirring occasionally, for a minute.
Pour in sweet and sour sauce. Cook, stirring occasionally, until the sauce thickens. Add tofu back in pan. Toss. Heat through.