Preparation Toss cauliflower with 1/4 cup oil, 1 teaspoon salt, and 1/2 teaspoon pepper in a large bowl, then divide between two 4-sided sheet pans. Roast cauliflower, turning it and switching position of pans halfway through, until just tender and browned in spots, about 20 minutes total. While cauliflower roasts, whisk together lemon juice, 1/2 teaspoon salt, and 1/2 teaspoon pepper in a large serving bowl, then add remaining 1/2 cup oil in a slow stream, whisking. Finely chop about 1 tablespoon capers, then whisk chopped and whole capers into vinaigrette. Add warm cauliflower and peppers and toss to coat. Serve at room temperature. Cooks' note:Peppers and cauliflower can be roasted and tossed with vinaigrette 1 day ahead and chilled.
Preparation Toss cauliflower with 1/4 cup oil, 1 teaspoon salt, and 1/2 teaspoon pepper in a large bowl, then divide between two 4-sided sheet pans. Roast cauliflower, turning it and switching position of pans halfway through, until just tender and browned in spots, about 20 minutes total. While cauliflower roasts, whisk together lemon juice, 1/2 teaspoon salt, and 1/2 teaspoon pepper in a large serving bowl, then add remaining 1/2 cup oil in a slow stream, whisking. Finely chop about 1 tablespoon capers, then whisk chopped and whole capers into vinaigrette. Add warm cauliflower and peppers and toss to coat. Serve at room temperature. Cooks' note:Peppers and cauliflower can be roasted and tossed with vinaigrette 1 day ahead and chilled.