Preheat your oven to 180C fan/gas mark 6. Trim the butternut squash and cut in half. Scoop out the seeds, then cut the squash into long thin boats. You will end up with around 8 slices. Place in a large roasting tray and drizzle with the olive oil. Lightly crush the coriander and cumin seeds, and sprinkle over the squash with the ground cinnamon. Season with sea salt and freshly ground black pepper and rub all the flavours into the squash. Lay the slices of squash out in the tray, skin side down if possible, and place in the oven. Roast for around 45–50 minutes, until the squash is charred but also tender.
While the squash is cooking, make the tahini dressing. Place the tahini in a bowl or jug. Peel and finely grate in the garlic. Squeeze in the lemon juice, season generously with sea salt and freshly ground black pepper. Add the 2 ice cubes, extra virgin olive oil and 2 tablespoons of cold water and blitz with a stick blender until you have a pale, whipped tahini dressing. Taste and adjust the seasoning.
Spoon on to a serving platter. Finely chop the coriander and stir through the roasted squash, then transfer to the platter and place on top of the tahini dressing. Drizzle over the chilli crisp oil and serve straight away.