In a wide skillet over medium heat, heat oil. Add potatoes and cook, turning as needed, until lightly browned. With a slotted spoon, remove potatoes from the pan and drain on paper towels.
Remove excess oil from pan except for about 2 tablespoons. Add onions, garlic, and ginger and cook until softened.
Add chicken and cook until lightly browned.
Add fish sauce and cook for about 1 minute.
Add coconut milk, water, and chili peppers. Bring to a simmer, skimming any scum that floats on top.
Lower heat, cover, and continue to cook for about 20 to 25 minutes or until chicken is cooked through and liquid is reduced.
Add potatoes and cook for about 3 to 5 minutes or until potatoes are tender and sauce is thickened.
Add bell peppers and cook for another 1 to 2 minutes or until tender yet crisp.
Season with salt and pepper to taste. Serve hot.