Wash and pat chicken dry with paper towel, sprinkle with pepper (fish sauce is very salty, no extra salt is necessary in this step)
In a medium saucepan, over medium heat combine water and chicken breast
Rough chop carrot, onion, fennel, and slice serrano chili in half lengthwise.
Peel and slice ginger
Smash garlic cloves, remove dry skin
Place all rough chop items in pot with chicken, stir to combine
Bring to a boil, reduce heat to medium, and cook covered for 35-40 minutes, stirring occasionally