You can place these in the oven simultaneously with the lamb; in fact, they can be arranged around the roast on the same pan.
4 medium red onions, peeled and halved (about 4 pounds)
2 teaspoons olive oil
1 teaspoon balsamic vinegar
3/4 teaspoon salt
1/4 teaspoon black pepper
How to Make It
Preheat oven to 400°.
Arrange onions, cut sides down, in a 13 x 9-inch baking pan or on a broiler pan coated with cooking spray. Combine oil and remaining ingredients in a small bowl; stir with a whisk. Drizzle onions with oil mixture. Bake at 400° for 1 1/2 hours or until very tender.