1. Preheat oven to 450°. Whisk together first 4 ingredients in a large bowl.
2. Toss red onions and next 3 ingredients with oil mixture. Arrange in a single layer on a lightly greased 17- x 12-inch jelly-roll pan. Bake at 450° for 30 to 40 minutes or until tender and golden brown, stirring twice.