Spinach and Mushrooms Salad with Orange Vinaigrette Recipe

1 teaspoon freshly grated orange zest
2 tablespoons fresh orange juice
2 tablespoons fresh lemon juice
1 teaspoon Dijon-style mustard
3/4 teaspoon salt, or to taste
2/3 cup olive oil
2 pounds fresh spinach, coarse stems discarded and the leaves washed well, spun dry, and, if desired, torn into bite-size pieces
1/2 pounds mushrooms, sliced

In a small bowl whisk together the zest, the juices, the mustard, and the salt, add the oil in a stream, whisking, and whisk the dressing until it is emulsified. In a large bowl toss the spinach and the mushrooms with the dressing.