1. Arrange onions on a jelly roll pan that has been smeared with olive oil.
2. Lightly sprinkle onions with olive oil (or you can use a spray, like Pam) and toss gently to coat. Sprinkle salt and pepper over the onions.
3. Bake uncovered at 400°F for 1⁄2 hour. Turn onion wedges over. Bake another 25 minutes or until tender. Place onions into a serving dish and drizzle with vinegar.