Heat your oven to 200°C/Fan 180°C/Gas 6. Scrub, trim and slice your carrots in half lengthways. Peel and trim the Jerusalem artichokes. Cut into 1cm-thick chunks. Break the cauliflower into small florets.
Tumble the veg onto a baking tray. Scatter over 1 tbsp cumin seeds. Drizzle over 1 tsp oil. Season. Put the garlic cloves (unpeeled) on the tray. Slide into the oven and roast for 25 mins.
While the veg roasts, tip the bulgar wheat into a heatproof bowl. Pour in 150ml boiling water. Season with a pinch of salt and pepper. Swirl to mix. Set aside, covered with a plate or cling film, to soak.
Peel the onion and cut into thick wedges. When the veg have roasted for 25 mins, remove the garlic from the tray. Add the onion wedges. Roast for another 15 mins.
Squeeze the roast garlic cloves from their skins using the back of a knife. Finely chop most of the coriander leaves and stalks, saving a few leaves for garnishing. Tip them into a bowl. Add the tahini and 4 tbsp cold water. Season well and mix to make a loose sauce. Set aside.
Take the veg out of the oven one last time. Scatter over the pumpkin seeds. Return to the oven for 5 mins. The veg should be charred and tender.
Uncover the bulgar wheat. Grate in the lemon zest and squeeze in the juice. Add a pinch of salt and stir to mix. Pile the veg and bulgar wheat up in bowls. Drizzle over the coriander sauce and serve, garnished with the remaining coriander.