Take prawns in a bowl. Add ginger-garlic paste, ¼ tsp crushed peppercorns, green chillies, salt, 6-7 chopped curry leaves, 1 tbsp molaga podi powder and mix well. Set aside to marinate for 10 minutes.
To make tempura batter, combine rice flour, cornflour, salt, ¼ tsp crushed peppercorns, 2 tsps molaga podi powder and drinking soda in a bowl. Whisk well into a smooth batter.
Heat sufficient oil in a kadai.
Dip marinated prawns in the batter and deep-fry in hot oil till golden and crisp. Drain on absorbent paper.
Cut pita breads into halves and slit to make pockets.
Finely shred lettuce leaves and place in a bowl. Add salt, remaining crushed peppercorns, 1 tsp molaga podi powder, 1 tbsp mayonnaise and lemon juice and mix well.
Heat 1 tsp oil in a non-stick pan. Add mustard seeds and let them crackle. Add remaining curry leaves and 1 tbsp molaga podi powder, mix and add some of the tempering to the remaining mayonnaise. Mix well.
Spread the tempered mayonnaise inside pita pockets. Place some lettuce mixture and stuff with 2-3 fried prawns.
Place prepared pita pockets on a serving plate. Spread some tempered mayonnaise on the sides and drizzle remaining tempering on top. Sprinkle 1 tsp molaga podi powder on top and serve immediately.