Finely chop mushrooms by hand or put in a food processor, use pulse button to finely chop. Heat oil in a non-stick frying pan over high heat. Add mushrooms, onion and garlic, cook, stirring often, for 8 minutes or until all moisture has evaporated. Stir in seasoning, cook 1 minute. Set aside to cool for 10 minutes. Drain any excess moisture and transfer to a bowl. Wipe pan clean.
Meanwhile, process chickpeas, parsley, haloumi, egg, breadcrumbs and half the tahini until almost smooth. Add to mushrooms, season and mix well.
Roll one tablespoonful of mixture into a ball, then roll lightly in sesame seeds. Place on a tray. Repeat to make 30 falafels. Cover and refrigerate 30 minutes if time permits. Mix remaining tahini and yoghurt together. Refrigerate until ready to serve.
Shallow or deep fry falafel in batches, turning often for 5 minutes or until golden. Serve warm or room temperature with tahini yoghurt, lemon and herbs.