4 red bell peppers, seeded and cut in half
2 heads cauliflower, trimmed and cut into 2-inch florets
1/4 cup plus 2 tablespoons extra virgin olive oil, divided
3 tablespoons fresh lemon juice
1 1/2 teaspoons salt, divided
1 teaspoon freshly ground black pepper, divided
2 tablespoons Spanish olives with chilies, chopped (optional)
Preheat oven to 400°F.
Cover bottoms of 2 large baking sheet pans with parchment paper.
Toss cauliflower florets and pepper halves with 2 tablespoons of olive oil, 1 teaspoon salt, and 1/2 teaspoon pepper in a large bowl, then divide between two 4-sided sheet pans. Roast vegetables, turning them and switching position of pans halfway through, until just tender and browned in spots, about 20 minutes total.
While vegetables roast, whisk together lemon juice, 1/2 teaspoon salt, and 1/2 teaspoon pepper in a large serving bowl, then add 1/4 cup of the olive oil in a slow stream, whisking. Add the chopped Spanish olives, if desired, into the vinaigrette. Add warm cauliflower and peppers and toss to coat. Serve at room temperature.
Note: Peppers and cauliflower can be roasted and tossed with vinaigrette one day ahead and chilled.