Open the can of tomatoes and pour the juice into a bowl. Use the lid to press against the tomatoes to extract as much juice as possible. In the can, avoiding cutting yourself with the rim, use your hand to squeeze the tomatoes to a pulp. Re-strain out the new juices, and reserve the juice and pulp separately. Fill the empty can half full with water and set aside.
Heat the olive oil in a heavy saucepan over medium-high heat. Add the onion and cook with a pinch of salt, stirring occasionally, until softened, about 2 minutes. Add the garlic and cook until golden. Add the tomato juices and bring to a boil. Simmer rapidly until the juice thickens, then add the crushed tomato pulp, oregano, the half can of water, bay leaf, and salt and pepper, to taste. Adjust the heat to maintain a simmer and cook, stirring occasionally to prevent scorching, until the mixture thickens and reduces to about 3 1/2 cups, about 30 to 45 minutes. Discard the bay leaf.