Heat oil, saute pearl onions until they turn transparent. (If the onions are big, cut it into 2-3 pieces). Add green chillies, ridge gourd, tomatoes, salt needed and cook until the ridge gourd turns soft. Leave it to cool. Grind it to a slightly coarse paste. Heat oil, add mustard seeds, when it splutters, add urad dal and curry leaves. When dal turns golden brown, add the seasoning to the chutney. Serve with idli, dosa or chapati.