In a wide pan over medium heat, heat oil. Add potatoes and cook for about 2 to 3 minutes or until lightly browned and tender. Remove from pan and drain on paper towels.
Add carrots and cook for about 1 to 2 minutes. Remove from pan and drain on paper towels.
Remove excess oil from pan except for about 1 tablespoon. Add bell peppers and cook for about 30 to 40 seconds. Remove from pan and set aside.
Add onions, garlic, and ginger and cook until softened.
Add chicken and cook, stirring occasionally until lightly browned.
Add fish sauce and continue to cook for about 1 minute.
Add coconut milk and water. Bring to a simmer, skimming any scum that may float on top.
Lower heat, cover, and simmer for about 20 to 30 minutes or until chicken is cooked.
Add potatoes and carrots and cook for about 3 to 5 minutes or until tender.
Add curry powder and stir to combine. Continue to cook for about 2 to 3 minutes or until sauce starts to thicken.
Season with salt and pepper to taste.
Add bell peppers and cook for about 1 minute or until tender yet crisp. Serve hot.