Before you start, preheat oven to 220°C (or 200°C fan bake).
Prep parsnip and kumara and toss on a lined oven tray with oil. Spread into a single layer, season with salt and roast on upper oven rack for about 25 minutes, until golden. Toss once during cooking.
Prep onion and beetroot. Cut buns in half lengthways, leaving a hinge. Set aside separately.
Heat oil in a large fry-pan on medium-high heat. Cook onion and beetroot with a pinch of salt for 6-7 minutes, until softened. Add caraway gravy mix and balsamic glaze and cook stirring for a further 1-2 minutes, until sticky. Season to taste with salt and pepper and set aside in a small heat-proof bowl. Wash and reserve pan.
Heat oil in reserved fry-pan on medium heat. Cook sausages for 6-8 minutes, turning often, until golden on all sides and cooked through.
Meanwhile, place buns on an oven tray and heat on lower oven rack for 4-5 minutes, until warmed through.
Serve buns filled with mustard, vegan aioli, rocket, sausages and relish. Serve veggie chips on the side.