Place chicken broth and asparagus in a medium saucepan over medium-high heat; bring to a simmer. Cook 8 minutes or until asparagus is tender. Remove from heat.
Heat butter and olive oil in a small skillet over medium-high heat. Add sliced shiitake mushrooms to pan; cook 3 minutes or until mushrooms begin to brown. Set aside.
Place bread on a baking sheet covered with foil; coat bread with cooking spray. Broil 2 minutes or until golden brown. Turn bread over, and sprinkle evenly with cheese. Broil 2 minutes or until cheese bubbles.
Pour asparagus mixture into a blender. Add rice, peppercorns, and salt; puree until smooth. Ladle 1/2 cup soup into each of 8 bowls; top evenly with mushrooms. Top each serving with 1 crouton.