Directions

• Preheat oven to 450°F. Bring 4 qts of water to a boil in a large Dutch oven over medium-high. Add green beans, and cook until crisp-tender, about 4-5 minutes. Drain beans, and plunge into a large bowl filled with ice water to stop the cooking process. Drain beans, and dry thoroughly with paper towels.
• Line a rimmed baking sheet with aluminum foil; lightly coat with cooking spray. Toss together mushrooms, 3 tbsp oil, 1/8 tsp salt, and 1/8 tsp pepper in a bowl; arrange evenly on prepared baking sheet. Roast at 450°F until mushrooms are deep brown and crisped, 12-15 minutes, stirring halfway through. Transfer mushrooms to a bowl; set baking sheet aside.
• Whisk together lemon juice, remaining ¼ cup oil, remaining 5/8 tsp salt, and remaining 3/8 tsp pepper in a large bowl until blended. Add beans; toss to coat. Gather beans into 10 bundles of about 20 beans each. Place bundle at the end of 1 prosciutto piece; roll up lengthwise. Repeat with remaining 9 bundles and remaining 9 prosciutto pieces.
• Arrange assembled bundles, seam side down, on reserved baking sheet. Bake at 450°F until beans are warmed and prosciutto begins to brown, 5-7 minutes. Transfer green bundles to a platter; sprinkle with roasted mushrooms.