1
To make the broth, heat the oil in a large saucepan over medium heat. Add the garlic and onions and cook, stirring, until softened, about 5 minutes.
2
Stir in the lemongrass, soup base, and ginger and cook for 2-3 minutes.
3
Add the water, lime leaves, and chile and bring to a simmer. Cover and simmer for 1 hour. Add the button mushrooms for the last 10 minutes of cooking time. Remove the lime leaves. Adjust the seasoning.
4
Bring a large saucepan of salted water to a simmer. Add the chicken breasts and poach until cooked through, 8-10 minutes. Transfer to a plate, cool slightly, then shred with two forks or your hands.
5
To assemble the soup, divide the shredded chicken between bowls. Ladle in the broth with mushrooms and garnish with lime wedges, cilantro, cherry tomatoes and chiles.