First, soak the tamarind in some water such that it gets soft and easy to grind.
Next, wash the cucumber well. Follow the everyday hack of chopping the ends of the cucumber and rubbing it slightly to remove the bitterness in it. Peel the skin and chop the cucumber finely. (retain the skin if you like the crunch)
Transfer the chopped cucumber into a mixing bowl.
Transfer the soaked and softened tamarind along with water to a mixer jar. Add in all the other ingredients mentioned under 'To Grind'. Add about 1/4 cup water and grind to a smooth paste. Do not make it very smooth and fine, a little finer than chutney should be enough. Also, DO NOT increase the quantities of mustard and cumin seeds, as they will make the gojju bitter.
Transfer the ground mixture into the bowl with chopped cucumber. Mix well, check for salt and add if required. Add more water if required to get the desired consistency. You can keep the gojju either thin or thick. I added a little less than 1/4 cup.
Prepare the tempering by heating oil in a small pan. Once it turns hot, add in the mustard seeds and let them crackle and splutter. Add in asafoetida and curry leaves. Turn off the heat and transfer the tempering to the prepared gojju. Mix it and serve it with rotti, dosae, chapathi or steamed rice.