Heat the oil in a medium sized pan on medium heat and add mustard seeds to it. When they start spluttering add kadipatta to it. Let it fry for around 20 seconds and then add onions and garlic paste and fry them till they are translucent. Add ground ajwain, pepper powder, and methi seeds and mix well.
Add tomatoes and fry them till they are mushy. [ If you are using tamarind instead, add tamarind paste and mix well and then move on to the next step]
Add the shrimp/prawn along with chili powder, salt, and Mangalorean masala powder and mix well. Then add half a cup of water and let the shrimp cook in it. Add water as needed till the shrimp is done and all there is no more water left.
Add grated coconut and mix well. Simmer it for 5 minutes and take it off heat and serve hot.