1 .Rub loin of pork with oregano and flour, then put it in a deep roasting pan and bake in a preheated 450°F oven for 30 minutes.
2. Add the chopped onions, carrots, and garlic and cook for an additional 15 minutes; reduce heat to 350°F and continue cooking for 30 minutes
3. Peel onions and potatoes and brown in a skillet, using the fat from the meat.
4. Add the onions and potatoes to the meat in the roasting pan and add enough water to half cover the vegetables.
5. Cover and roast in a 350°F oven for at least 1 hour. Cook until meat thermometer reads 180°F.
6. Meanwhile saute mushrooms in butter.
7. Arrange meat on a platter and surround with vegetables.