Rinse, pat dry and slice mushrooms. In a medium saucepan combine vinegar and mushrooms; bring to a boil. Reduce heat and simmer, covered for 2 mins. Drain mushrooms; set aside to cool. In a small saucepan bring water to boil. Add carrots & celery; return to boil. Reduce heat and simmer covered for 3 mins. Add red, green peppers; cover and simmer for 3 mins or until tender. Drain and set aside to cool. In medium bowl mix olive oil, oregano & salt, black pepper; let stand 10 mins. Stir in mishrooms, carrots, and other vegetables. Mix well. Cover and refrigerate at least 2 hrs. before serving.