Preheat the oven to 425° F. On a baking sheet, tossed together the cauliflower, olive oil, paprika, cumin, cardamom, turmeric, cayenne, lemon, garlic, and a large pinch each of salt and pepper. Bake 15 minutes, toss and bake another 15 minutes, until lightly charred.To make the zhug. Combine all ingredients in a food processor or blender. Pulse until finely chopped. If the sauce is too thick, add water, 1 tablespoon at a time to thin. Taste and add more salt as needed. To assemble, stuff/spread each pita with zhug, then lettuce, roasted cauliflower, and red onion. Drizzle over more zhug. Add tahini and harissa, if desired (recipes in notes).