Heat the oil in a frying pan over a medium heat. Add the meatballs and cook for 5 minutes, turning so they cook all over. Add the red onion and cook for a further 5 minutes, until the onion is soft and the meatballs are cooked through.
Toast the pittas and slice open on one side.
Take to the table and let everyone spoon in their own filling of tzatziki, salad, mint,tomatoes and meatballs, and serve with the lemon wedges to squeeze over the filling.
Cook’s tip: these make great food on the go. Cut the tops off the pittas, stuff with filling, wrap in cling film and keep in a cool bag until ready to eat.