Dip oysters in egg whites; dredge in breadcrumbs. Set aside.
Pour oil into a large heavy skillet; heat to 350°. Fry oysters, in batches, about 1 minute on each side or until golden; drain on paper towels.
Arrange mushrooms evenly over spinach, and drizzle with half of Red Wine Vinaigrette. Top salads with oysters, onion slices, and bacon, and serve immediately with remaining vinaigrette.