1. Preheat oven to 400°.
2. Arrange bread slices on a baking sheet; coat with cooking spray. Bake at 400° for 5 minutes or until golden brown and toasted; cool.
3. Combine radishes and next 4 ingredients (through salt) in a medium bowl, and toss to coat.
4. Spread each bread slice with about 2 teaspoons cheese; top with a single layer of arugula and a layer of radish slices.