Heat a barbeque to a high heat, or preheat oven to 400 degrees F (200 degrees C).
In a 9x13 inch baking dish combine olive oil, vinegar, garlic salt, rosemary, and ground black pepper. Place carrots, potatoes, and onions into the dish and toss to coat.
Bake or grill, turning occasionally, until tender (approximately 40 minutes).
