In a large bowl, dissolve yeast in warm water. Add the oil, sugar, salt and 2 cups flour. Beat until smooth. Stir in enough remaining flour to form a soft dough (dough will be sticky).
Turn onto a lightly floured surface; knead until smooth and elastic, about 6-8 minutes. Place in a greased bowl, turning once to grease the top. Cover and let rest in a warm place for 10 minutes.
Divide dough in half. On a floured surface, roll out each portion into a 10-in. circle. Transfer to two greased 12-in. pizza pans; build up edges slightly. Bake at 425° for 10-12 minutes or until golden brown.
Meanwhile, in a small bowl, combine the tomato sauce, onion, garlic, salt and pepper; spread over crust. Sprinkle with Parmesan cheese and oregano. Arrange pepperoni over top; sprinkle with mozzarella cheese. Bake 10-15 minutes longer or until cheese is melted.