In a 10-inch broiler-proof or regular skillet heat oil; add potatoes, onion, garlic, 1/4 teaspoon of the salt, and the pepper. Cover and cook over medium heat for 5 minutes. Turn potato mixture with a spatula. Cover and cook for 5 to 6 minutes more or until potatoes are tender, turning mixture once more.
In a medium mixing bowl beat together eggs, oregano, and the remaining salt. Pour egg mixture over hot potato mixture. Sprinkle with olives. Cook over medium heat. As the mixture sets, run a spatula around the edge of the skillet, lifting egg mixture to allow the uncooked portion to flow underneath. Continue cooking and lifting edges until egg mixture is almost set (the surface will be moist).
Place the broiler-proof skillet under broiler 4 to 5 inches from the heat. Broil for 1 to 2 minutes or until top is set. (Or, if using regular skillet, remove the skillet from the heat; cover and let stand for 3 to 4 minutes or until the top is set.) Sprinkle the top with finely shredded provolone or Parmesan cheese. Serve immediately. To serve, cut frittata into wedges. Makes 4 servings.