
In a pot over medium heat, heat oil. Add onions and garlic and cook until softened.
Add beef and cook, stirring occasionally, until no longer pink.
Add fish sauce and continue to cook for about 1 to 2 minutes.
Add tomatoes and cook until softened and begins to release juice.
Add water and bring to a boil. Lower heat, cover and cook for about 1 to 1 1/2 hours or until tender.
Add chayote and cook for about 7 to 10 minutes or until tender.
Season with salt and pepper to taste. Serve hot.