To prepare vinaigrette, cook bacon in a medium nonstick skillet over medium heat until crisp. Remove bacon from pan, reserving 1 teaspoon drippings in pan. Crumble bacon; set aside. Add vinegars, honey, mustard, salt, and pepper to drippings in pan, stirring with a whisk; bring to a boil. Remove from heat.
To prepare salad, combine onion, pears, spinach, and bacon in a large bowl. Drizzle with vinaigrette, and toss gently to coat.