Heat oil in a pan. Add the fish heads and fry them till golden.
Take them out and keep them aside.
Now, add the chopped Garlic and onion in the same oil and fry them till light. now add the diced vegetables and stir them for 2-3 minutes till they turn tender.
Now, add the Malabar spinach greens. if you find your pot too full before you add the whole of greens, allow them to wilt before adding the rest.
Season with some salt and add the green chilies and fried fish heads. Cover the pan and allow it to release the water and cook in it. It should take somewhere around 15-20 minutes to fully cook the vegetables and stalks of Malabar Spinach or Pui Saak.
Once cooked, remove the lid and cook on medium-high heat to reduce the water completely. Break the fish heads further using the spoon.
Once it dries out completely, and starts releasing oil from the edges turn the heat off and serve.