Customize the flavors to your personal preference. The heat and sour level is what ever you want!
Heat pot on medium high heat. Add oil and once oil is hot, add onion and garlic. Cook until translucent.
Add cooked chicken breast, fresh ginger and fish sauce. Stir and cook the soup for about 1 minute until everything is fragrant. Add chicken stock, Kaffir lime leaf, lemongrass, bell pepper, tomatoes, and chili pepper.
Bring the soup to a boil, then simmer on low for about 5 minutes. Remove from heat and add the fresh lime juice right before serving. Adjust the soup to your personal taste by adding additional salt or fish sauce. Garnish with chopped cilantro. Enjoy!
Note 1: Different brands of fish sauce have different levels of saltiness, so adjust accordingly. Taste the broth and if you want the soup more salty, add more fish sauce. Or add more water to make it less salty.
Note 2: If you want the soup more spicy, add more chili peppers and if you want it more sour, add more fresh lime juice.