Heat oil in a pan. Add onions, chillies and curry leaves. Mix well. Add salt and mix well.
Now cover and cook on a low heat till onions are transparent. Now cook on a low heat till the onions are caramelized. It will take around 15 to 20 mins.
Once the onions are well cooked. Add in turmeric powder and mix.
Add in tomatoes and cook till mushy.
Add in garam masala and chilli powder. Cook for few more mins.