Preheat the broiler. Toss the carrots and turnips with 1 tablespoon olive oil, 1/2 teaspoon salt and a few grinds of pepper in a large bowl, then spread on a rimmed baking sheet. Broil, tossing halfway through, until tender and charred in spots, about 12 minutes.
Meanwhile, heat the remaining 1 tablespoon olive oil in a large nonstick skillet over medium-high heat. Add the pancetta and cook, stirring occasionally, until browned and crisp, about 6 minutes. Add the shallot, thyme and a pinch each of salt and pepper; cook until the shallot is just translucent, 1 to 2 minutes. Stir in the oats and grated beet; cook, stirring, until the oats are lightly toasted, about 1 minute. Add the chicken broth, 1/4 cup water, a pinch of salt and a few grinds of pepper. Simmer, stirring often, until tender and saucy, 12 to 15 minutes.
Divide the risotto among bowls. Top with the roasted vegetables and parsley.