For the black bean sauce, place the beans in a colander and rinse under cold running water. Drain well. Tip the beans into a small bowl and mash with the back of a fork or spoon to form a rough paste. Add the remaining ingredients and mix well.
Place a wok or large frying pan over high heat. When hot, add a good drizzle of oil and swirl the wok or pan to coat the surface. Add the green beans and cook for about 2 minutes. Add 2 tablespoons of black bean sauce, along with about 3 tablespoons of water, and toss for another 1-2 minutes, until the beans are bright green and tender-crisp. Taste and season with sea salt and black pepper if necessary—you could add more black bean sauce if you wish. Sprinkle with the sesame seeds and serve with rice.
