Combine lemongrass, ginger and stock in a soup pot. Heat to simmering, add broccoli and cabbage, and bring to a boil. Reduce the heat and allow it to simmer for about 5 minutes. Stir in coconut milk, lime juice and tamari. Just before serving, add the basil (or cilantro), soy noodles (or cubes of tofu), plus hot sauce to taste. Garnish with thin strips of hot chili peppers if desired.