Preheat the oven to 400 F
Trim the leaves off of the cauliflower and rinse well. Bring a large pot of water to a boil and boil the cauliflower for 20 minutes. Drain and place onto a baking sheet
Drizzle the cauliflower with olive oil, and rub the za'atar, cumin and salt all over the cauliflower until evenly coated. You can flip the cauliflower over so that its easier to rub the bottom pieces.
Lightly drizzle the seasoned cauliflower, then bake for 40-45 minutes. You can set it under the broiler for the last 2 minutes.
While that bakes, add all of the tahini ingredients to a blender and blend until smooth. If it's too thin, add in 1 more tbsp of tahini. If you prepare this ahead of time and refrigerate it, you may need to add 1-2 more tbsp of water to thin it out.
Once the cauliflower is cooked and you're ready to serve it, pour some of the tahini sauce onto your serving plate, then top if with the cauliflower. Finish it off with more of the tahini, sesame seeds and chopped parsley.
Leftover tahini sauce will stay fresh in the fridge for a week.