Finely chop the onions and make a puree of the tomato.
Now, heat the oil in a pan. (as mentioned, use 2 tablespoon oil from the pan, which was used for frying the meatballs.
Sprinkle the red chilli powder and turmeric powder into the oil and mix thoroughly.
Now add the onion and fry those till it changes color.
Now add Tomato Puree, followed by Ginger paste, garlic paste, and also green chilli paste.
Mix properly.
At this point, add salt and sugar and cook till the oil comes from the side of the mixture.
Now mix the Madras Curry Powder with 1 tablespoon water to make a thick paste.
Add this thick paste to the pan and mix thoroughly.
Once mixed, add ⅔ of the coconut milk and mix properly.
Now add 2 more cups of water and bring the mixture to boil.
The mixture should have a nice red color.
Once the mixture starts boiling, add the meatballs and cook for 20 minutes on a low flame.
You should check the curry and if needed add water.
At this point, add 1 tablespoon Lemon juice to it.
Once properly cooked, add the remaining coconut milk and also the garam masala, and give it a light mix.
You can add some cilantro as well.