Bring a medium pot of water to a boil and blanch green beans until tender-crisp, 2 to 3 minutes. Drain and put in a large heatproof bowl.
Bring 2 1/2 cups water to a boil in another medium pot with vinegar, sugar, salt, chiles, peppercorns, and kombu. As soon as liquid boils, pour over beans and add lemon. Let cool to room temperature. Slit 3 of the chiles to let seeds spill into liquid. Chill, covered, overnight to let flavors develop. Serve cold. Keeps, chilled, up to 1 week.
*Find in grocery stores' Asian foods aisle.
Note: Nutritional analysis is per 1/4-cup serving.