Heat the oil in a large skillet over medium-high heat and brown the roast on all sides. Transfer the roast to a heavy casserole. To the fat remaining in the skillet, add the onions, celery, carrots, and garlic. Cook, stirring frequently, until tender, about 10 minutes. Add the tomato paste and stir to coat the vegetables; transfer to the casserole. Pour the wine into the skillet and scrape up any browned bits; add the contents of the skillet to the casserole, along with the mushrooms, salt, oregano, and tomatoes (plus 1 cup of their liquid). Cover the casserole and cook in a 300° F oven for 3 hours or until the meat is very tender, adding more of the tomato liquid if necessary.