Preheat oven to 425 degrees F. Line a baking sheet with parchment paper.
Prepare the cauliflower by removing the leaves and trimming the stem without slicing it off. Cut the cauliflower lengthwise from the head through the core, making 1.5-inch slices that resemble flat "steaks." Depending on the size of your cauliflower, you may slice between 4 and 6 flat pieces.
Transfer the cauliflower steaks to the lined baking sheet. Brush each side with olive oil and sprinkle with salt and pepper. Bake for approximately 25 to 30 minutes, flipping the cauliflower halfway through.
While the cauliflower is roasting, prepare the tahini sauce. Combine all ingredients in a mixing bowl, and whisk. It will stiffen up, so add up to ¼ cup water slowly, and whisk to get a runnier sauce that can be easily drizzled.
When the cauliflower is finished, transfer to a serving plate and drizzle with sauce. Enjoy!
Serve with a side salad or steamed vegetables. You may have some leftover sauce, which you can keep in an airtight container in the fridge and use as a veggie dip.
You will likely have some stray cauliflower florets after you cut the steaks. You can toss them in olive oil, salt, and pepper, and roast them on the same sheet as the steaks. Eat them on their own with the leftover sauce or add them to salads.