Cube your leftover idlies and deep fry them in hot oil till golden. Drain them in some paper towel.
Now make the masala. Heat oil and add in some fennel and curry leaves.
Now add in onions, green chillies and cook them for a couple of mins till they turn golden.
Now add in salt and sugar and mix them well.
Add in ginger garlic paste and cook them for a min.
Add in chilli, coriander, turmeric, garam masala powder and mix well.
Add in tomato puree, tomato ketchup and cook them for 5 mins.
Add in peas and cook them for 5 more mins.
Pour in some water and mix them well.
Add in the fried idly pieces and toss well with the masala.
Press them firmly in the masala and simmer for 5 more mins.
Add in coriander leaves and lemon juice.
Mix them around. Serve immediately with onion raita.