For the Dough
For dough, stir flours with salt in a large bowl and cut in butter (with fingers or a pastry cutter) until mixture is a rough crumbly texture.
Beat together egg, water and vinegar in a small bowl with a fork. Add to flour mixture, stirring with fork until just incorporated.
Turn out mixture onto a lightly floured surface and gather together, then knead gently once or twice, just enough to bring dough together. Form dough into a disc, wrap and chill for at least an hour.
For the Filling
For filling, heat oil in a sauté pan over medium heat. Add chicken, cumin, coriander and chili powder and sauté until chicken has cooked through.
Remove from pan and increase heat to medium high. Add onion and peppers and sauté for 1 minute. Add garlic, ground coriander and chili powder and cook for 1 minute more.
Add mixture to chicken and stir. Season to taste, stir in chili flakes (if using) and let cool, then stir in fresh coriander.
Preheat oven to 190°C and line a baking tray with parchment paper. On a lightly floured surface, roll out dough into a rectangle about 1/4-inch thick.
Cut out 12 squares (3 by 4) (they should be about 6-inches across). Spoon about 1/3 cup filling into centre of each.
Fold pastry over to make a triangle and pinch together, fluting the edges and place on baking tray. Re-roll dough if necessary.
Brush turnovers with eggwash and bake for 20 to 25 minutes, until golden brown. Serve warm or at room temperature.