Preheat the oven to 425° F.
Toss the onion and red pepper with your olive oil and sea salt; spread onto a parchment lined sheet-pan, and roast until beginning to caramelize, 10-12 minutes.
In a large sauté pan, add the cooked pasta, roasted vegetables, harissa paste, ⅓ cup of the reserved starchy pasta cooking water, and the Cashewmilk Yogurt. Stir well to combine and bring to a simmer to heat through, adding additional pasta water until the desired consistency is achieved. Season to taste with salt and pepper and toss in the basil leaves at the very last minute. Serve immediately.