Preheat oven to 400 degrees. Begin by par-boiling the whole cauliflower in a large pot of salted boiling water for approximately 15 minutes. To know when it's done, when poked with a fork, the cauliflower should give a little resistance. Remove cauliflower from the pot and drain excess water.
In a round baking dish, drizzle the bottom with olive oil to prevent the cauliflower from sticking. Place cauliflower in the dish.
Prepare the roasting seasoning by combining olive oil and za'atar to form a paste. Brush paste all over the top and sides of cauliflower. Roast for 30 minutes.
Remove from oven, drizzle with tahini, top with parsley, and slice into your healthy pie o' heaven.