Soak tamarind in half cup of water for about 10 minutes. Extract it's juice discarding the residue. In a cooking vessel or pan add all the chopped pieces of Mangalore cucumber and half cup of water. Cook these pieces along with tamarind extract, jaggery, turmeric powder and curry leaves till the pieces turn pulpy.
Meanwhile heat a wok adding oil followed by black gram lentils, chickpea lentils, red chillies, coriander, cumin, fenugreek seeds and curry leaves. Roast all these ingredients in medium flame till the lentils turn little brown. Transfer all the roasted ingredients in to blender and grind it to coarse paste along with grated coconut. Add water as required.
When the Mangalore cucumber pieces on stove have cooked well, add the ground coconut paste and salt. Combine everything well. Include water to get the curry to desired consistency and bring it to boil. Switch off once done.
Heat a seasoning pan with all the seasoning ingredients included, as the mustard seeds start to crackle transfer it to curry.
Authentic Mangalore cucumber curry is ready to serve with steamed rice.