Marinate the shrimp in lemon juice for 15 minutes. Heat oil in a pan and add fenugreek and mustard seeds. When it pops add the onion and fry until golden. Add garlic, red chili powder, turmeric powder, coconut and yogurt and mix well. Stir-fry for 2 minutes. Now add the shrimp and salt, fry for couple of minutes and cover the pan. Cook over medium heat for 10 more minutes or until the shrimp is cooked. Stir occasionally to prevent the mixture from sticking to the bottom of the pan. Serve hot.