In a pressure cooker add Green gram (mung bean), tomato, onion, green chili, garlic, 1/2 lemon juice and 1 to 1 1/2 cup water (or as needed) and cook for 3 whistle. Remove from heat and keep aside until the pressure is gone. Add salt as needed and mix well.
In a pan heat oil, add mustard seed, split black gram, cumin seed, curry leaves and cook until the mustard seed stop splattering. Now add this to the pressure cooked Dal.