Preheat oven to 350°.
Combine first 5 ingredients in a bowl; cover buttermilk mixture, and chill.
Coat both sides of bread with cooking spray. Place on a baking sheet, and bake at 350° for 5 minutes on each side. Spread 1/2 teaspoon pesto on one side of each slice of bread.
Combine greens and remaining ingredients in a large bowl; toss well. Add buttermilk dressing; toss well to coat. Serve with crostini.