Add vegetable oil to a deep-frying pan on the stovetop, and heat over medium heat.
Add cubed potato and cook for one minute, frequently stirring using a wooden spatula. Transfer to a bowl and keep covered.
Return the pan to the stove. Over medium heat, add the minced garlic, chopped onion, and grated ginger, and sauté until fragrant and soft.
Add chicken breast strips and cook until slightly golden.
Drizzle the fish sauce over it and continue cooking for another minute.
Gently pour in the coconut milk and water, and then season with curry powder. Stir the mixture using a wooden spoon.
Cover the pan with a lid, reduce the heat to low to medium heat, and simmer until half the liquid evaporates.
Add the chopped bell pepper, green chili pepper, and cooked potato. Sauté for 2-3 minutes.
Season with salt and pepper as needed.