In a wide pan over medium heat, heat oil.
Add potatoes and carrots and cook, turning once or twice, until lightly browned. Remove from pan drain on paper towels.
Remove excess oil except for about 1 tablespoon. Add bell peppers and cook for about 30 to 40 seconds. Remove from pan and drain on paper towels.
Add onions and garlic and cook until softened.
Add chicken and cook, turning as needed, until lightly browned.
Add fish sauce and cook for about 1 to 2 minutes, stirring as needed.
Add tomato sauce and reserved juice from canned pineapples (about 1 cup). Bring to a boil.
Lower heat, cover, and simmer for about 20 to 30 minutes or until chicken is cooked through.
Season with salt and pepper to taste.
Add potatoes, and carrots, and continue to cook until vegetables are tender and sauce is thickened.
Add green peas, pineapple chunks, and bell peppers and cook for another 1 to 2 minutes or until heated through.