Clean the mushrooms and cut them into chunks. Heat the olive oil in a sauté pan over medium heat. Add the garlic slices and cook for 2-3 minutes or until they are lightly browned. Remove the garlic. Add the mushrooms to the pan. Cook for 4-5 minutes or until they have softened. Remove to a bowl and let cool. Toss with the vinegar. Season to taste with salt. Serve at room temperature.