Preheat your oven to 400 degrees F. With a large sharp knife, cut your squash in half vertically and remove the seeds with a spoon, cut in half again vertically, making 4 vertical pieces of squash per squash. We won't be peeling our honeynut squash, as you can eat the peels!
Line a large sheet pan with parchment paper and transfer your squash to the baking sheet. Drizzle 1/4 cup olive oil onto the honeynut squash on all sides. Then sprinkle the harissa powder, salt, and pepper. Toss completely to combine, placing your squash in a single layer, flesh side down.
Transfer to the oven on the lower rack and roast for 30 to 40 minutes, depending on the size of your squash, flipping halfway.
In the meantime, make your Tangy Pistachios. In a medium bowl, mix the toasted and chopped pistachios with your remaining olive oil, red wine vinegar, salt, and pepper. Whisk continuously until emulsified and all combined.
Once your squash is fork tender and roasted, transfer to a serving platter, and pour over a heaping drizzling of your Tangy Pistachios, finishing with a pinch more of harissa powder to serve.