Heat enough oil. Add the mustard seeds, urad dal, cumin seeds and curry leaves, and fry till the splutter. Add the chopped onion, cook until it turns translucent.
Add the slit green chillies, saute for few seconds.
Add the cabbage pieces and salt. Cook everything on low heat without adding water - close the kadai with lid.
Stir the vegetables occasionally. Once the cabbage gets well cooked, put off the stove. Add the cooked rice to the already cooked vegetables and the lemon juice. Toss everything gently for few seconds.