Roasted Cauliflower and Radicchio Salad

Put oven rack in middle position and preheat oven to 450 °F. Toss cauliflower with 1/4 cup oil, 1/2 teaspoon salt, and 1/8 teaspoon pepper in a large bowl. Spread in 1 layer in a shallow baking pan (1 inch deep) and roast, turning over with tongs halfway through roasting, until tender and golden brown, 25 to 30 minutes total. Cool in pan on a rack, then transfer to large bowl. Whisk together vinegar, shallot, remaining 1/4 teaspoon salt, and remaining 1/8 teaspoon pepper in a small bowl, then add remaining 5 tablespoons oil in a slow stream, whisking until emulsified. Add half of dressing to cauliflower and toss to coat. Add romaine, radicchio, parsley, half of nuts, and remaining dressing to cauliflower and toss to coat. Season with salt and pepper and sprinkle with remaining nuts.