Preheat oven to 375 degrees Fahrenheit. Cut potato into ¼-inch thick slices and spread out in a lightly oiled baking dish. Sprinkle parmesan cheese over potato. Chop the onion. Cut garlic into thin slices. Heat olive oil in a frying pan, sauté onion and garlic for about 1 minute. Add oregano, mix and sauté for another minute. Spread this mixture evenly in the baking dish. Cut cherry tomatoes into halves and plate on top of everything already in the baking dish. Bake 30 to 40 minutes or until potato is soft.