Place potatoes in a medium size saucepan and cover with lightly salted water. Bring to a boil; simmer for 15 to 20 minutes until fork-tender. Drain and set aside.
In a small bowl, whisk together vinegar, olive oil, oregano, thyme and 1 teaspoon of steak seasoning. Set aside.
Heat broiler. Spray a large broiler pan with nonstick cooking spray.
Thread potatoes, mushrooms and beef on 8 metal skewers. Place on prepared broiler pan and brush generously with the oil and vinegar mixture. Season with 1/2 teaspoon of steak seasoning. Broil on middle rack for 5 minutes; turn, brush with remaining vinegar and oil mixture and season with remaining 1/2 teaspoon steak seasoning. Broil for additional 5 minutes or until vegetables are tender.
Serve with salad if desired.