Bring a pot of heavily salted water to a boil. Add the whole cauliflower head and boil until tender, flipping the cauliflower halfway through, about 10 to 12 minutes total. Remove and let drain.
Heat oven to broil on high. Place it on a baking sheet and drizzle with the olive oil. Season with salt and pepper
Broil until the cauliflower is lightly charred on the top, about 5 minutes, checking occasionally.
Add cauliflower to a mixing bowl and break into smaller pieces with tongs.Top with the tahini, zhoug, green onions, sesame seeds, tomatoes, and diced radishes, tossing to combine.
Pile into the warmed pitas with pickled onions and arugula and serve.