Fugazzeta (Argentinian Stuffed Pizza) - Tara's Multicultural Table

Name: Fugazzeta (Argentinian Stuffed Pizza) - Tara's Multicultural Table
Cuisine: European, Italian, Mediterranean
Ingredients: Dough; 3/4 cups water, lukewarm (105-115 degrees F); 1/4 cup milk, lukewarm (105-115 degrees F); 2 1/2 teaspoons active dry yeast; 2 3/4 cups bread flour; 2 teaspoons sugar; 1 teaspoon salt; 1 tablespoon extra virgin olive oil, plus more for greasing bowl; Filling and Topping; 2 tablespoons extra virgin olive oil, plus more for greasing and drizzling; 2 medium onions, thinly sliced; 1 teaspoon dried oregano; Salt to taste; Crushed red pepper flakes to taste; 1 pound mozzarella cheese, grated, divided