In a large skillet over medium heat, add the ground beef, chopped onion, and minced garlic. Cook until the meat is browned and the onion is translucent, about 5-7 minutes. Drain excess fat if necessary.
Stir in the Italian seasoning, salt, and pepper, and then add the marinara sauce. Mix well and let it simmer for another 3-4 minutes.
Remove the skillet from heat and add the mozzarella and cheddar cheese to the meat mixture. Stir until the cheeses melt slightly into the mixture.
Roll out the pizza dough on a floured surface into a large circle. Transfer it to a greased pie dish or a shallow baking dish, allowing the edges to overhang.
Pour the meat and cheese mixture into the center of the dough, spreading it evenly. Top with pepperoni slices.
Fold the edges of the dough over the filling and pinch to seal. Brush the top of the dough with an egg wash (whisked egg) for a nice golden finish.
Create small slits on the top of the pie to allow steam to escape.
Bake in the preheated oven for 25-30 minutes, or until the crust is golden brown and cooked through.
Remove from the oven and let it cool slightly before slicing. Garnish with fresh basil leaves if desired.