Combine sweet potato, onion, 2 tablespoons olive oil, and 3/4 teaspoon salt in a large bowl; toss to coat. Arrange vegetables in a single layer on 2 lightly greased baking sheets.
Bake at 450° for 35 minutes or until browned, removing onion after 25 minutes, and stirring sweet potato.
Meanwhile, cook bacon in a large nonstick skillet over medium heat 12 minutes or until crisp. Drain bacon, reserving 2 tablespoons drippings in pan.
Add remaining 1/4 cup olive oil, remaining 3/4 teaspoon salt, vinegar, mustard, and pepper to drippings in skillet. Stir well. Transfer vinaigrette to a large bowl. Add roasted sweet potato, onion, pecans, and raisins, tossing gently to coat. Cool.
Note: If you have only one oven, place 1 baking sheet on the lower oven rack and 1 on the upper rack; switch positions after 25 minutes. Bake 5 to 10 more minutes or until potatoes are browned.