Preheat oven to 400°F and line a baking sheet with parchment paper or a silicone mat. Toss cauliflower with oil in a large bowl. Spread in a single layer on the prepared baking sheet. Roast until tender and just starting to brown, 20 to 25 minutes. Let cool to room temperature.
Add the cauliflower, garlic, tahini, lemon zest, lemon juice, salt, cumin, crushed red pepper and water to a food processor. Process until combined, scraping down the sides of the bowl as needed. Add more water, if desired, to make a looser dip.
Transfer to a bowl. Drizzle with additional olive oil and sprinkle with chopped pepper, if desired.
Parchment paper or silicone baking mat
Roast cauliflower (Step 1) and refrigerate in an airtight container for up to 2 days.