Wash, peel off the skin and dice the cucumber. Heat oil in a sauce pan and toast mustard, cumin and curry leaves until it splutters. Add onion, chillies and ginger garlic paste and saute until brown, add chopped tomatoes and cook till they turn soft and mushy. All dry masala powders like turmeric, red chilli powder, dhania powder and salt can be added along with diced cucumber. Partially close the pan with a lid and cook for 5 to 8 minutes on meduim flame. Once it turns tender and soft, garnish with corrainder and serve with hot rice and ghee.