Preheat the oven to 425°F degrees and line a large baking sheet with parchment paper.
Add the cauliflower and olive oil to the prepared baking sheet. In a small bowl, whisk together cumin, paprika, coriander, garlic powder, salt and pepper, and sprinkle it on the cauliflower. Use your hands to toss the cauliflower with the seasoning on all sides.
Bake until the cauliflower is golden brown and fork tender, about 40 minutes, tossing halfway through.
To assemble the pitas, place lettuce and tomatoes in the pita pockets, add the roasted cauliflower on top and drizzle with the tahini sauce.
Notes
Storage: Store everything in the fridge in separate containers and then assemble the pita sandwiches when you're ready to eat.