You can marinate the paneer or chicken for upto 24 hours.
For a vegan version, replace the paneer with chickpeas in the shawarma spice mix, and then roast them for 15-20 minutes at 250°C. Alternatively you can also use sliced portobello mushrooms. Omit the yogurt sauce or make it with dairy-free yogurt.
For gluten free, use gluten free pitas.