In a large bowl, combine the flour, salt, sugar, and instant yeast. Mix well.
Gradually add the warm water and olive oil to the dry ingredients. Stir until a dough forms.
Knead the dough on a floured surface for about 5-7 minutes until smooth and elastic.
Place the dough in a greased bowl, cover with a clean towel, and let it rise in a warm place for about 1 hour or until doubled in size.
Preheat your oven to 400°F (200°C).
In a separate bowl, mix together the diced ham, mozzarella cheese, ricotta cheese, garlic powder, and oregano until well combined.
Once the dough has risen, punch it down and divide it into 4 equal pieces. Roll each piece into a circle about 6 inches in diameter.
Spoon a portion of the ham and cheese mixture onto one half of each dough circle, leaving a small border around the edge.
Fold the other half of the dough over the filling and press the edges to seal. Use a fork to crimp the edges for a decorative touch.
Place the calzones on a baking sheet lined with parchment paper. Beat the egg and brush it over the tops of the calzones. Sprinkle with Parmesan cheese if desired.
Bake in the preheated oven for 20-25 minutes or until golden brown.
Allow to cool for a few minutes before serving.