Heat the oil in large soup pot, make a refrito or base for the soup by adding the diced onion and crushed garlic, cook until the onions are soft, about 5 minutes.
Add the 8 cups of water and bring to a boil.
Add the diced green bananas to the boiling water.
Cook over medium high heat, stirring occasionally, until the bananas or plantains are soft, about 15-20 minutes. It will take longer for the plantains to cook than the bananas.
In the same pot, gently mash some of the bananas pieces to help thicken the soup.
Crumble the cheese and add it to the soup
Stir in milk or cream, cilantro and salt
Remove from the heat and serve with slices of avocado, cheese and aji or hot sauce.
Notes
For a creamier variation of this green banana or green plantain soup, add 1-2 small potatoes, peeled and diced, when adding the green bananas to the soup. Adjust the amount of water or milk to your preferred consistency or thickness.