In a large soup pot or small stockpot, combine the chicken stock, lemongrass and ginger and bring to a boil. Reduce the heat to a simmer and cook for 5 minutes. Squeeze lemon halves, then add with red onion, potatoes, corn, andouille, and garlic. Simmer broth about 8 to 10 minutes.
Increase the heat so that the mixture comes to a boil and add the clams. Cover and cook, stirring occasionally, until the mixture returns to a boil and the clams open and just cooked through, 4 to 6 minutes. Serve the clams in shallow bowls, paying attention to remove any lemongrass or ginger pieces, with some of the cooking broth ladled over the clams. Garnish with the chopped cilantro.