Heat oven to 475 F.

Toss squash with oil and spread on baking sheet lined with foil or parchment. Sprinkle with salt and pepper, and roast until squash is tender, about 20 minutes. Transfer to platter.

In small bowl, whisk together tahini, garlic, lemon, water, cayenne and salt and pepper to taste. Sprinkle grapes over squash and drizzle with tahini sauce. Sprinkle with zaatar and serve.