Preheat the oven to 180°C, place the grapes on a baking tray and top with the zest of ½ the lemon. Drizzle with olive oil, season with a little salt and pepper and cook for 15 minutes.
Add the walnuts to the tray and roast for 5-10 minutes until the grapes are caramelised and the walnuts are golden.
Add the mustard, apple cider vinegar, honey and yoghurt to a bowl and mix well before adding the chopped thyme and the juice of ½ a lemon.
Spiralize the celeriac and apples, and sprinkle with the juice of the remaining ½ a lemon to keep them fresh.
Roughly tear the lettuce leaves and line the bottom of the bowl with them, before adding the spiralized celeriac and apple and topping with the caramelized grapes and chopped red onion.
Drizzle with the mustard dressing and toss well, finishing it off with roasted walnut pieces and crumbled gorgonzola.
