Preheat the oven to 410°F (210°C) with convection mode on.
Cut the cauliflower into florets, rinse, and soak in a bowl of water for a few minutes. Drain and pat dry.
Toss the cauliflower with olive oil, salt, black pepper, and chili flakes. Spread on a baking sheet and roast until golden brown, about 25 to 30 minutes.
In a bowl, mix ½ cup raw tahini with ¾ cup cold water, ½ medium juiced lemon, and ½ teaspoon salt. Spread a generous layer of tahini dressing on a serving plate. Arrange the roasted cauliflower on top, then spoon over the seasoned crushed tomatoes. Drizzle with more tahini and a bit of olive oil.
Sprinkle with chopped parsley and, if using, toasted pine nuts. Finish with a pinch of coarse salt to taste. Serve warm or at room temperature.