Heat oven to 400°F. Make Arepas: In large bowl, stir flour, water and 1/4 teaspoon salt with spoon; let rest about 1 minute or until mixture thickens. Stir in mozzarella cheese. Shape 6 balls of dough, using about 1/3 cup dough each. Place each ball on plastic wrap; shape each into 4-inch circle, 1/2 inch thick. In 12-inch nonstick skillet, heat 1 tablespoon oil over medium heat. Cook arepas in oil about 4 minutes on each side, until dark spots appear on both sides. Place arepas on ungreased cookie sheet. Bake about 20 minutes or until fully cooked and hollow sounding when tapped. Keep warm.