Bring a small skillet of water to boil. Blanch prosciutto until fat is melted; drain and pat dry. Wipe skillet dry, add ½ tablespoon of the olive oil, and heat over medium. Add prosciutto and cook until browned and crispy. Transfer to paper towels to drain.

In a large bowl, combine ice and cold water.

Bring a large saucepan of salted water to boil. Add broccoli florets and cook for 1½ minutes; add mixed vegetables, fennel, mushrooms, scallion, bell pepper and cabbage. Continue cooking 1 minute more; drain vegetables and transfer to ice water. Drain and pat dry. Arrange on a plate with prosciutto.

Whisk together walnut oil, broth, mustard, vinegar and remaining tablespoon olive oil. Season with salt and pepper to taste, drizzle over vegetables and serve.