In a pot over medium heat, heat oil. Add bananas and fry until lightly browned. Remove from pan and drain on paper towels.
Add potatoes and fry until lightly browned. Remove from pan and drain on paper towels.
Remove excess oil except for about 2 tablespoons. Add onions and garlic and cook until softened.
Add chicken and cook, stirring occasionally, until lightly browned and juices run clear.
Add fish sauce and cook for another 1 to 2 minutes.
Add tomato sauce and water and bring to a boil, skimming any scum that accumulates on top.
Lower heat, cover, and cook for about 15 to 20 minutes or until chicken is cooked.
Add potatoes and cook until tender.
Add chorizo de bilbao, garbanzo beans, and bananas. Cook until heated through.
Add green beans and napa cabbage and cook for another 2 to 3 minutes.
Add pechay and cook for about 1 minute or until vegetables are tender yet crisp. Serve hot.
Season with salt and pepper to taste.