Put the beetroot in the centre of a large piece of foil with the garlic cloves and thyme sprigs. Drizzle over the oil and season with the black pepper.
Seal the foil into a parcel and place on a roasting tray. Roast in the oven for 45 minutes or until soft. Squeeze the garlic from their skins and toss with the beetroot. Leave to cool completely.
Whisk together all the dressing ingredients.
Carefully toss the rocket with the beetroot and smoked salmon and divide onto serving plates. Drizzle the dressing over each plate to serve.
Notes
If you have a chef's blowtorch, singeing the orange segments provides a slight toasted flavour.