How to Make It
Remove stems from mushrooms. Slice mushroom caps to equal 4 cups. Heat oil in a large nonstick skillet over medium heat. Add shallots; cook 3 minutes. Add mushrooms and garlic; cook 4 minutes, stirring occasionally. Sprinkle flour over mushroom mixture; cook 30 seconds, stirring constantly. Stir in broth, thyme, and pepper; cook 3 minutes or until sauce thickens, stirring frequently.
Place polenta on a baking sheet coated with cooking spray; broil 4 minutes on each side or until thoroughly heated. Top with mushroom mixture; sprinkle with cheese.