Preparation Place chicken and spinach in large bowl. Cook bacon in large skillet over medium-high heat until crisp. Using slotted spoon, transfer bacon to paper towels. Pour off all but 3 tablespoons drippings from skillet. Add onion and vinegar to drippings in skillet; stir to heat through, scraping up browned bits, about 1 minute. Pour dressing over chicken and spinach. Add bacon; toss to coat (spinach will wilt slightly). Season salad with salt and pepper; serve.
Preparation Place chicken and spinach in large bowl. Cook bacon in large skillet over medium-high heat until crisp. Using slotted spoon, transfer bacon to paper towels. Pour off all but 3 tablespoons drippings from skillet. Add onion and vinegar to drippings in skillet; stir to heat through, scraping up browned bits, about 1 minute. Pour dressing over chicken and spinach. Add bacon; toss to coat (spinach will wilt slightly). Season salad with salt and pepper; serve.