Slice chicken into thin strips and marinate with one tablespoon of curry paste, salt, and pepper.
Fry chicken in oil over high heat for five minutes until cooked and set aside.
Fry onions in remaining oil for three minutes, then cover and cook for ten minutes to soften.
Add ginger and remaining paste, then stir in flour, coconut milk, fish sauce, and sugar.
Add lemon grass, lime leaves, and chicken to the pan and simmer for five minutes.
Boil sugar snap peas for two minutes, drain, and refresh in cold water.
Discard lemon grass and lime leaves from the curry broth.
Stir in lime zest, juice, water chestnuts, and peas before serving with rice.