Preheat your oven to 400F and line a baking sheet with foil or parchment. Spread the squash in an even, single layer on the sheet. Drizzle the avocado oil over the squash and mix it with your hands to coat. Sprinkle the squash generously with salt and pepper. Transfer the squash to the oven. Roast the squash for 30 minutes, stirring the pieces on the sheet halfway through roasting, or until the squash pieces are turning golden at the ends and tender.
Line another baking sheet with parchment. In the last 5 minutes of the squash's roasting time, place your seeds of choice on to the second baking sheet and transfer the seeds to the oven to toast. They should toast in 5-7 minutes; the aim is for them to be just golden, as they'll continue to cook for a few minutes after you remove them from heat.
While the squash cooks, fit a pot of boiling water with a steamer attachment. Steam the kale for 3 minutes, or until it's just tender. Remove the kale from heat.
Whisk the harissa tahini ingredients together, starting with 2 tablespoons of water. Continue adding just enough water as needed to create a thick, yet pourable dressing.
To serve right away, transfer the roasted squash to a mixing bowl. Add the steamed kale. Pour about 1/4-1/3 cup of the dressing over the ingredients and fold everything together gently. Divide the squash and kale mixture into bowls. Top with the toasted seeds and an extra drizzle of the dressing right before serving. Alternatively, you can store the separate components in airtight containers in the fridge, and assemble them into bowls when ready.