Preheat the oven to 180C/gas 4. Heat a roasting tin and sear the pork fillet. Season and remove from the heat. Add the garlic, rosemary, olive oil and lemon juice. Roast in the oven for 25 minutes. Remove and rest for 10 minutes. Carve into slices. You can also bbq it.
For the salad: put the leaves, onion, tomato and cucumber in a large bowl. Add the tzatziki and a squeeze of lemon juice and mix well.
Heat the pitas by lightly wetting and then lightly oiling each side. Place in a frying pan heating either side gently.
Slice through the top of the pitta and spread some humous on the inside. Then fill the pitta with the pork and salad mix. Halve each ptta to serve.