In a glass measuring cup, mix together olive oil, sugar, red wine vinegar, celery seed, minced onion, dried mustard, paprika, and salt. Pour into a medium cruet with a tight fitting lid. Set aside until ready to use. Shake well before using.
To prepare the spinach salad, cook bacon and boil eggs. Slice eggs, mushrooms, and carrots as directed.
In a large bowl, combine spinach, mushrooms, carrots, bacon, boiled eggs, and croutons. Toss well. Right before serving, drizzle dressing over salad. Toss to coat. Sprinkle with freshly ground black pepper as desired. Makes 6-8 servings.