How to Make It
Heat oven to 425° F. On a large rimmed baking sheet, toss the Brussels sprouts and cauliflower with 2 tablespoons of the oil and ½ teaspoon each salt and pepper. Roast, tossing once, until tender, 20 to 25 minutes.
Meanwhile, heat the remaining tablespoon of oil in a large skillet over medium heat. Season the chicken with the herbes de Provence, ½ teaspoon salt, and ¼ teaspoon pepper. Working in batches, cook until golden brown and cooked through, 2 to 3 minutes per side, adding more oil as necessary. Serve with the vegetables.