Preheat oven to 200 degrees C. Grease two baking trays.
For the filling, cook potato and carrot in boiling water for 5 minutes. Add peas and cook for a further 2 minutes. Drain well; tip the vegetables into a bowl. Stir in curry paste, coriander and salt; mash the mixture very slightly to combine. Leave to cool.
Take 1 sheet of pastry (keep the other one covered to prevent it drying out) and cut it crosswise into 6×30cm long strips. Brush them with a little of the oil.
Lay a pastry strip lengthwise in front of you; place 1 rounded tbsp filling in the middle of the end nearest to you. Lift one end corner and fold it diagonally over filling to make a triangular shape, flattening the filling slightly. Continue folding the strip over in a triangular shape until you come almost to the end. Trim off any excess pastry. Repeat with the remaining filo pastry and filling to make 12 triangles.
Place filo triangles on baking sheets, brush with remaining oil and scatter crushed coriander seeds over the top. Bake for 10–15 minutes or until golden.
To make the salsa, cut mango cheeks from both sides of the stone, then peel and cut the flesh into small dice. In a serving bowl, combine with ginger, lemon juice, sugar, chillies and oil. Serve with hot filo triangles.