Peel off the jackfruit seeds and cook them till soft with some water.
Take the cooked jackfruit seeds in a mixer jar, add cumin seeds, salt, grated coconut and red chillies. Grind all of them together to fine paste with required water.
Pour this puree in to a bowl, mix with enough buttermilk. Let the consistency of tambli to be like rasam.
Heat a seasoning pan and include all the seasoning ingredients in the order mentioned, as the mustard seeds crackle transfer it to the tambli.
Notes
The jackfruit seeds should be cooked to very soft or mushy. You can use pressure cooker too to cook them.
This tambli is very mild not spicy. You can increase the chillies to make it bit spicier.
Red chillies can be substituted by green chillies or black pepper.