Prepare the sauce. Put the cornstarch in a small bowl. Slowly add the stock, mixing as you do so. Now add the chilli paste, soy sauce, sesame oil, salt and sugar. Mix again set sauce aside.
Heat the vegetable oil in a wok over a medium high flame. When hot, put in the garlic and ginger and stir-fry for 10 seconds. Add the spring onions, stir-fry for 5 seconds. Put in the tofu and fry for 1 minute. Turn heat to low, stir the sauce and pour it over the tofu. Mix gently and bring to a simmer. Let the sauce thicken, stirring gently every now and then as it does so. Serve with rice.