Drain the tofu well on kitchen paper and cut into 2cm cubes. Combine the cornflour, crushed Sichuan peppercorns and sea salt flakes on a small tray. Add the tofu and mix well to coat on all sides.
Heat the sunflower oil in a wok or deep-sided frying pan. The oil is hot enough when a small piece of bread sizzles and browns in about 30 seconds. Cook the tofu in the hot oil, in batches, until crisp. Drain on kitchen paper and set aside. Quickly cook the cashews in the hot oil until golden, and add to the tofu. Carefully pour off all but 1 tbsp of the oil from the pan.
In a small saucepan combine the rice vinegar, caster sugar, soy sauce, sliced chilli, chilli flakes, ginger and garlic. Simmer over a medium heat for 2 minutes.
Peel the carrot and cut it into batons. Cut the fine beans in half on the diagonal. Return the wok to a medium-high heat, add the carrots and beans, and stir-fry for 1-2 minutes until tender. Add the tofu, cashews and chilli dressing, and cook for another 1-2 minutes until bubbling and hot through.
Scatter with the sliced spring onions and serve.