Shawarma shrooms with green sauce

Name: Shawarma shrooms with green sauce
Ingredients: 750g/1lb 10oz mushrooms, roughly chopped or torn; 2 tbsp shawarma seasoning; 4 tbsp vegetable oil; 4 wholemeal pittas or flatbreads, lightly toasted, to serve; 100g/3½oz Iranian cucumber pickles, drained and chopped, to serve (optional); ½ lemon, juice only; ½ small red cabbage, thinly sliced; salt; 60g/2¼oz fresh flatleaf parsley; 3 heaped tbsp light tahini; 2 heaped tbsp full-fat Greek-style yoghurt; 250g/9oz plum tomatoes, cut in half; 1 small cucumber, seeds removed and chopped; 1 small red onion, finely chopped; 100g/3½oz pomegranate seeds; 1 lemon, juice only; 1 tsp sumac