Whisk together the remaining ingredients for the romanesco in a small bowl then pour into the bowl with the florets. Toss to combine.
Spread out onto a baking sheet in a single layer and roast for 10 minutes. Stir to toss the romanesco on the pan and roast for an additional 10 minutes. You can broil on high for the last 1-2 minutes for extra crispy edges if desired.
While the romanesco roasts, make the tahini sauce by combining all the ingredients except water in a bowl. Whisk until smooth then drizzle the water in slowly while whisking until a sauce-like consistency results. It should be drippable but not too thin. Add or subtract water as necessary for desired result.
Serve the roasted romanesco with the tahini sauce while hot.