Heat the oven to 200°C/400°F. Spread the squash out on a baking sheet, drizzle with 1 tablespoon of the olive oil and add 2 tablespoon of the harissa. Toss to coat the squash in the harissa. Put the squash in the oven and roast for 30-40 minutes until soft and charred around the edges.
Whisk together the remaining harissa and olive oil and season with salt and pepper. Put the rocket in a bowl and toss with the dressing. Spread on a serving plate and spread over the avocado slides and butternut squash. Sprinkle over the goat's cheese then dot over the Greek yoghurt and serve. Sprinkle with nigella seeds if desired.
Nutrition information is an estimate and will vary depending on the exact ingredients used.