Preheat oven to 425° F. On a baking sheet, combine the cauliflower, 4 tablespoons olive oil, garlic, shallots, paprika, chili powder, oregano, turmeric, and a pinch each of salt and pepper. Toss well to evenly coat. Transfer to the oven and roast for 15 minutes, or until tender. Toss and roast another 10 minutes, until lightly charred.On a separate large baking sheet, toss the sweet potatoes with 2 tablespoons olive oil, seasoned salt, and a pinch of pepper. Bake 15 minutes, toss, then bake another 10 minutes until the potatoes are crispy.Meanwhile, combine the cucumbers, avocado, lemon, dill, salt, and pepper.To assemble, add lettuce to a bowl. Top with cauliflower, sweet potatoes, cucumber/avocado, feta, and any other desired toppings. Add a few dollops of Tzatziki sauce. Drizzle over the tahini. Serve with pitas.