For the Marinade: In a blender, combine the ginger with the water and blend until smooth, add a little more water as needed to blend. Strain the mixture through a fine strainer to extract the ginger juice and discard the rest. Marinate the chicken with the juice and place in the refrigerator.
For the paste: Blend all the ingredients in a blender until smooth, 2 to 3 minutes.
Heat oil in large saute pan or small wok over medium high heat. Add paste and stir to render for about 20 seconds. Add coconut milk, salt, sugar, and fish sauce and stir to cook for 2 minutes.
Add sliced chicken and stir to mix well and cook for 2 minutes longer. Add the green beans and hot chili-flakes and cook until the chicken is thoroughly cooked. Serve with steamed jasmine rice.