- In a pan over medium heat, heat oil.  
- Add potatoes and carrots and cook, turning once or twice, until lightly browned. Remove from pan and drain on paper towels.  
- Remove excess oil from pan except for about 2 tablespoons. 
- Add bell peppers and cook for about 10 to 15 seconds. Remove from pan and drain on paper towels. 
- Add onions and garlic and cook until softened.  
- Add chicken and cook, turning on sides once or twice, until lightly browned. 
- Add tomatoes and cook, mashing regularly with back spoon until softened and release juices.  
- Add fish sauce and simmer for about 30 to 40 seconds. 
- Add water and bring to a boil.  
- Lower heat, cover, and cook for about 15 to 25 minutes or until chicken is tender and sauce is slightly reduced. 
- Add potatoes and carrots and continue to cook until fork-tender. 
- Add bell peppers and sweet peas. Cook for 1 to 2 minutes or until green peas are heated through and bell peppers are tender yet crisp.  
- Continue to simmer until sauce is reduced to desired consistency. Season with salt and pepper to taste. Serve hot.