Line a baking tray with baking paper. Preheat the oven to 200°C top/bottom heat.
Cut away any coarse dirt from the outside of the Hokkaido. Otherwise, leave the skin on.Remove the seeds from the squash and cut it into compact pieces that are not too small. Spread the pumpkin pieces on the baking tray, cover with the spice mixture and oil, and mix with your hands.
Place the baking tray in the oven and roast for 30 minutes.
Meanwhile, peel, halve and deseed the cucumber. Then grate it coarsely. Mix with salt, place in a sieve and leave to drain for 15 minutes.
Peel and crush the garlic cloves, mix with the yoghurt. Stir in the lemon juice.
Squeeze the grated cucumber well and add to the yoghurt. Mix everything together and season with salt and pepper to taste.
At the end of the roasting time, remove the baking tray from the oven. Season the pumpkin with a little salt if necessary.
Arrange the pumpkin and tzatziki on a serving plate. Garnish with lamb's lettuce and parsley, drizzle with a little olive oil and sprinkle with coarsely ground pepper.