Whisk the stock, juice, soya sauce, sugar and cornflour in a small bowl until smooth.
Heat 2 tsp oil in a large wok over medium-high heat. Add garlic, ginger and chillies. Stir-fry 30 seconds. Add to stock mixture.
Heat remaining oil in frying pan. Add capsicum and spring onion. Stir-fry until crisp-tender, 2 to 3 minutes. Add corn and cabbage. Stir-fry 1 minute. Add tofu and stock mixture. Cover and simmer 2 minutes. Serve at once.