In a large bowl, whisk together 1 cup flour, yeast, sugar, oregano, salt, and garlic powder.
Add water and olive oil, mixing together until blended well.
Gradually add 1/2 cup of flour at a time until a soft, but somewhat sticky dough ball is formed. Add more flour if necessary.
On a lightly floured surface, knead the dough until smooth and elastic for about 4 minutes, adding additional if necessary.
Preheat the oven to 375 degrees.
Prepare two baking sheets by lining them with parchment paper.
Roll out the dough so that it is about 1/8 – 1/4-inch thick. Using a 4 1/2-inch round cookie cutter, cut circles into the dough. Re-roll the dough and cut into more circles if possible.
Place one of the dough circles on a plate. Brush the outer edge of the circle with the beaten egg.
On one side of the dough, layer 4-5 pieces of pepperoni leaving a little of the brushed egg on the edge exposed.
Cover with 1-2 tablespoons shredded mozzarella. Carefully fold the dough over cheese and pepperoni bringing the egg brushed edges together.
Seal the edges by crimping them with a fork. With a sharp knife, cut three vents in the top of the calzone.
Repeat process with remaining dough circles, pepperoni, and cheese and place finished calzones on the prepared baking sheets.