Heat oil in a pan and sauté chopped onions until soft and light golden.
Add ginger-garlic paste and green chilies, cook for 1–2 minutes.
Add chopped prawns and cook on medium flame until they turn pink.
Add mustard paste, turmeric, and salt. Mix well.
Cook until the mixture becomes slightly dry and well combined.
Turn off the heat and let the filling cool.
Fill the prawn mixture into samosa sheets and fold into triangle shapes.
Deep fry in hot oil until crispy and golden brown.