Place a wok over a high flame, pour in the cooking oil and, when it’s hot, add the garlic and ginger and stir-fry for about 30 seconds, or until fragrant. Add the bird’s-eye chillies and stir, then mix in the black beans and the soaking liquid. Cook until sizzling, then add the clams, the banana chillies and about 60ml (¼cup) of hot water. Stir well, then cover the wok with the lid and turn the heat to medium. Cook for several minutes, or until the clams are cooked, stirring occasionally. If needed, stir in a little more water (the clams will give off a lot of liquid). The clams are ready when the shells open.