Add the walnuts to a small baking sheet and put into the oven. Bake for 10-12 minutes, or until toasted, then remove from oven.
Increase oven temperature to 450 degrees.
Let walnuts cool, then chop roughly.
Cut off cauliflower leaves, and cut out hard core of cauliflower. Chop the rest of the cauliflower into florets, about 2 inches in size.
Put cauliflower florets in a bowl and toss with olive oil, salt, and pepper.
Line a baking sheet with parchment paper or nonstick foil, and add cauliflower in a single layer. Roast cauliflower for 15 minutes, stir, then roast 5-10 more minutes, until cauliflower is tender.
While cauliflower is roasting, whisk together yogurt, tahini, 1 tablespoon of lemon juice, and soy sauce. Taste sauce, then season with salt and pepper. Add more lemon juice, a teaspoon at a time, to create the flavor you like. Add the water a tablespoon at a time, until the sauce is loose enough to drizzle over the cauliflower.
Garnish with chopped toasted walnuts to serve.
Notes
Storage Tips: Roasted cauliflower can be kept in an airtight container in the refrigerator for 3-5 days. Keep any leftover tahini sauce in a separate container in the refrigerator—a small mason jar works great. Leftover walnuts can be kept out at room temperature for about a week in a container or baggie.Expert Tips: The time required to roast your cauliflower will partly depend on how big you cut the florets. And, note that you don’t need to use foil or parchment paper if you have a well-seasoned sheet pan like I do! You’ll get better browning without the paper.Make sure you stir your tahini well before using it, as it has a tendency to separate in the jar. Also, note that some tahini products are much thicker than others—that will impact how much water you have to add to make your tahini lemon sauce. And, if you want a super smooth sauce, try blending it in a food processor.