Place the sliced onions in a bowl of cold water. This will make them crisp and less raw onion tasting. Leave them in the water for about 30 minutes
Next make the dressing. You'll need a jar with a tight fitting lid to mix it.
Combine 1/2 cup olive oil, 2 tablespoons of Balsamic vinegar, 2 teaspoons of whole-grain mustard, and 1 teaspoon each of sugar and sea salt. Add a little freshly ground pepper, secure the lid on the jar and shake the dressing vigorously until it's blended. Remove 2 tablespoons of the dressing and place in a bowl. Set the rest aside.
Add 1/3 cup of dried cranberries to the 2 tablespoons of dressing and set aside. This will soften the dried cranberries and make them easier to chew.
Wash the spinach and pat dry. Remove stems as needed.
When you're ready to serve the salad grab a large bowl, add 8 cups of fresh spinach, sliced onions, and pears. Give dressing in the jar a good shake and pour it over the salad. Scatter in the cranberries on top and toss everything well to coat with dressing.