Wash and soak moong dal in enough water for at least 30 minutes. Make sure it is soaked thoroughly.
Add water to a pressure cooker, add chopped beans to a bowl without adding any water. Place this bowl in the pressure cooker and cook for 2 whistles.
Heat a pan with oil, add mustard, jeera and curry leaves, let them splutter, then add hing and ginger if using, saute.
Add tomatoes, salt and turmeric. Fry the tomatoes till they turn fully mushy. After that cook for another 2 mins.
Add the dal, beans, chili powder and salt as needed.
Mix well and fry for 2 to 3 mins. If there is any stock left after cooking beans, just pour it and increase the flame to evaporate that water.
Close the lid and cook for 2 to 3 mins till the beans turn tender and blend well with the tomato and chili powder. Also make sure dal is cooked fully.
Add coriander leaves, coconut if desired. beans curry is ready.