Wash dal and rice and drain the water. Heat oil in a pressure cooker. Add cumin seeds, ginger, and garlic. Then add onions. Fry for a few minutes till onions are golden brown. Add green chillis.
Add dal and rice to the pressure cooker along with 6 cups cold water. Add salt, cumin powder, and chilli powder. Cook khichdi in pressure cooker. Wait for 3 whistles, lower heat to simmer, and cook 10 more minutes.
When cooker has released pressure, open the lid. Add another cup of water to the khichdi. Stir well, and cook on low heat till water is absorbed, about 5 minutes. Add ghee, mix well. Serve immediately. If you like, add a teaspoon of ghee on each serving. Serve with kadhi, raita, or plain curd with pickle and papad on the side.