Preheat the broiler.
Put the tomato soup, water, and garlic into a large pot and bring it to a boil over high heat. When it is boiling, add the macaroni, green onions, oregano, and pepperoni and stir well. When the macaroni is cooked, about 6 to 8 minutes, pour the soup into oven safe bowls. Top each with 1/4 cup mozzarella and 1/4 cup Cheddar. Sprinkle on some oregano and put under the broiler until the cheese is bubbling and lightly browned, about 3 to 5 minutes.
Alternately, you can serve the soup in a small round, crusty loaf of bread. Cut the top off the bread and scoop out the insides. Fill with soup, top with the cheeses, and broil per the directions above.