Drain the chickpeas and pat dry with kitchen paper. Tip into a food processor along with the onion, 2 of the garlic cloves, parsley, cumin, coriander, harissa paste, tahini, flour and a little salt. Pulse to combine. It should not be pureed smooth. Shape into four patties with your hands.
Heat the oil in a non-stick frying pan, and fry the burgers for 3 mins on each side until lightly golden.
While the patties are cooking, make the garlic aioli. Chop the remaining cloves of garlic very finely and mix it together with the mayonnaise, milk and lemon juice and stir to a smooth, creamy sauce.
Cut the pita bread in half and trim one half slightly so that it fits inside the other half to create a more durable pocket.
When the patties are finished cooking, stuff two patties into the half-cut pita bread, and top with shredded lettuce, sliced cucumber, sliced red onion. Drizzle with the aioli and enjoy!
Note: This is a very high fiber recipe, but also quite high in carbohydrates. If you are a diabetic and need to manage your carb intake, we suggest using only half of one pita, rather than doubling them as Chef Kris suggests. These patties would also be delicious served over a salad for a lower-carb option.