Preheat your oven to 425 °F (220 °C).
In a small bowl, whisk together all the marinade ingredients (oil, lemon, paprika, cumin, allspice, turmeric, tamari, agave, garlic, salt, and pepper).
Place the sliced mushrooms and onions on a baking sheet, then pour the marinade on top. Now, gently toss with your hands to coat everything well. Let it sit for 15 minutes while you prepare the tahini sauce and let the oven heat up. This will give the marinade time to soak in.
In a small bowl, whisk together the tahini, lemon, agave, garlic, cumin, and salt. It'll be really thick and will somewhat seize up which is normal. Now, slowly pour the water in and whisk until creamy and smooth. Add more water as needed for desired consistency. It should be somewhat thin like a pourable dressing. Taste for flavor and adjust if needed. Place in the fridge until ready to serve. It may thicken up in the fridge, so just add a splash of water and stir.
Spread the marinated mushrooms out in an even layer on the baking tray and place them in the oven. Let them roast for 10-15 minutes until tender and golden. Rotate the pan midway through. Keep an eye on them to prevent burning. Taste and add more seasoning or a squeeze of lemon if needed.
When the mushrooms have a few minutes left, place the pitas on the oven rack to warm up. Watch carefully because they can turn crispy really fast. They just need 1-2 minutes in the oven.
To serve, spread hummus (if using) on the warm pitas, then add the mushrooms, pickles, tomatoes, cabbage/lettuce, mint, or parsley. Drizzle with tahini sauce. Serve immediately. Enjoy!