Quick Roasted Carrots and Cauliflower with Walnuts

4 medium carrots (about 12 ounces), peeled and thinly sliced on an angle 1 small head cauliflower (about 2 1/4 pounds), trimmed into small florets 4 teaspoons extra-virgin olive oil 1/4 teaspoon dried thyme Kosher salt and freshly ground black pepper 1 ounce finely chopped walnuts (about 3 tablespoons) 2 tablespoons chopped fresh parsley 1/2 teaspoon finely grated lemon zest