1.Make dressing. Combine ingredients in a small bowl; season to taste.
2.Preheat oven to 200°C/400°F.
3.Scrub beetroot and carrots. Divide beetroot, carrots and onion between two baking-paper-lined oven trays. Spoon half the dressing over vegetables; toss to coat. Season. Roast vegetables 45 minutes or until tender. Cool slightly; peel beetroot.
4.Meanwhile, make goat’s cheese twists. Place one pastry sheet on a work surface. Brush with egg, then sprinkle with chives, seeds and cheese. Top with remaining pastry sheet, pressing down to secure. Using a small sharp knife, cut pastry into 16 x 1.5cm (¾-inch) wide strips. Twist strips; place on a baking-paper-lined oven tray. Bake 15 minutes or until golden and puffed.
5.Stir mustard into remaining dressing.
6.Arrange rocket on plates or a large platter; top with vegetables, mint, nuts and remaining dressing. Serve warm salad with twists.
Dressing can be made 3 days ahead; store in the refrigerator. Twists can be made a day ahead; reheat on an oven tray at 180°C/350°F for 5 minutes. If you have any goat’s cheese leftover, sprinkle it over the salad.Note