How to Make It
Preheat oven to 425°F.
Combine onion, 2 tablespoons oil, 3/8 teaspoon salt, 1/4 teaspoon pepper, green beans, and mushrooms on a foil-lined baking sheet. Bake at 425°F for 15 minutes or until browned.
Bring cauliflower and next 5 ingredients (through garlic) to a simmer in a saucepan over medium; cook 25 minutes or until tender. Remove pan from heat. Carefully place cauliflower mixture in blender; blend until smooth. Return puree to pan; stir in remaining 1/2 teaspoon salt, remaining 1/2 teaspoon pepper, sherry, and nutmeg.
Place green bean mixture in an 11- x 7-inch baking dish coated with cooking spray; top with cauliflower mixture. Combine remaining 2 tablespoons oil with bread; sprinkle over dish. Bake at 425°F for 10 minutes.