Preheat the oven to 400ºF (200ºC). Line a baking tray with baking paper.
Cut the cauliflower into small florets – You can either separate the florets with your hands or slice the it widthwise with a knife.
Put it in a baking tray, drizzle with olive oil, paprika and salt, and toss it with your hands.
Spread the cauliflower on the tray and roast it for 10 minutes, then using a spatula flip the cauliflower and continue to roast for 5 - 10 minutes, until the cauliflower is golden-reddish and tender.
Meanwhile prepare the tahini
Put the tahini butter in a small bowl. Squeeze inside the lemon juice. Stir gently with a spoon until the tahini butter begins to thicken and harden. Gradually stir in some water until the texture is smooth and velvety. Put it aside.
Chop the parsley and arugula (or cilantro or scallion instead) and finely dice the onion.