For the challah: In a small bowl, combine yeast, sugar and water. Whisk to dissolve, then add eggs and salt and whisk again. Place yeast mixture into the bowl of a stand mixer fitted with a dough hook. With mixer on medium speed, gradually add flour. When dough holds together, it is ready for kneading.
Turn dough onto a floured surface and knead until smooth. Place dough in a bowl lightly greased with vegetable oil. Cover with plastic wrap and let rise in a warm place for 45 minutes, or until almost doubled in size.
For the turkey filling: In a medium cast-iron skillet over medium heat, add olive oil. When shimmering, add ginger and onion and saute until browned, 3 to 4 minutes. To the skillet, add turkey, pistachios, raisins, cinnamon, and chili powder. Saute until turkey is cooked through, 8 to 10 minutes. Set aside to cool.
For the everything spice: Place the onion flakes, dried garlic, salt, caraway seeds, poppy seeds and sesame seeds in a bowl; mix and set aside.
To assemble: Preheat the oven to 375 degrees F.
Turn dough onto a floured surface and roll into a rectangle approximately 1/8-inch thick. Cut into 3-inch squares. Spoon 2 tablespoons turkey filling on top of each square. Fold up the sides to form dumplings and crimp the tops. Place top-side down on a baking sheet, leaving about 2 inches between each pastilla. In a small bowl whisk egg with 1 tablespoon water. Brush pastillas with the egg wash, then sprinkle with the everything spice.
Bake until golden brown, about 25 minutes. Cool, then dust with powdered sugar and serve.