Preheat oven to 425 degrees F. Trim cauliflower and cut florets into ½" pieces. Toss on a baking sheet with the olive oil, salt, and pepper, and roast until tender when pierced with a fork and golden brown, 20 to 25 minutes.
Meanwhile, whisk together the yogurt, lemon, and garlic.
Arrange a layer of lettuce on a large platter and then sprinkle the pomegranate seeds and cooked cauliflower on top. Finish with dollops of dressing and salt and pepper.