Meatloaf without marmalade breasts

5 tablespoons olive oil 3 large onions , coarsely chopped 1 tablespoon sugar 2 teaspoons dried oregano 2 garlic cloves , minced 1/4 cup apple cider vinegar 1[...]

2 slices white bread 1 1/2 lbs ground sirloin 1 1/2 cups finely chopped button mushrooms 1 cup shredded part-skim mozzarella cheese 1/3 cup finely chopped[...]