Heat oil in a wok or skillet over medium-high heat. Saute onions and add the potatoes then cook with cover until potatoes are half cooked.
Add the shredded chicken, carrots, red bell pepper and stir several times. Add the water and season with salt and pepper. Let it simmer while stirring occasionally until almost all liquids are gone. Lastly, add the green peas and raisins and cook for another few minutes until all liquids are gone. Transfer the cooked filling in a colander to remove any excess liquid. Set aside to let cool before using.
In a mixing bowl mix together the flour, baking powder, sugar, and salt. Cut in butter using the mixer by pulsing until mixture resembles coarse meal, with a few pea-size pieces of butter remaining. Add water, a tablespoon at a time, pulsing until dough is no longer too crumbly and holds together when squeezed. Squeeze the dough together to form a ball. Cut the dough into 4 equal parts.
Take a piece of the dough and roll it out to flatten to not more than half-centimeter thick. Cut out disks using a large cookie cutter or any round object with the desired size ( I use a small glass bowl). Do the same with the remaining dough. Gather all excess dough cuttings and press together and repeat the process until all dough is used.
Place a dough disk on your palm and spoon enough empanada filling in the center. Fold in half towards the edges and pinch the sides to close. Use a fork to press and seal the sides tight.
Place empanadas on a baking sheet lined with parchment paper in a single layer. Brush each empanada with the egg wash to make them shiny and brown after baking. Poke (3-5) small holes on each empanadas using a toothpick or fork to let the steam out and prevent them from bursting open while baking.
Bake at 360°F/180°C for 18-20 minutes. Empanadas are done when they appear light brown and shiny.