Preheat oven to 220°C/ gas mark 7. Combine all falafel ingredients except one tablespoon olive oil in the bowl of a food processor. Process for ten seconds. Stop motor and scrape down sides of bowl, then pulse for another ten seconds, until all ingredients are well incorporated but mixture is still slightly coarse and grainy.
Form mixture into 16 falafel balls and brush with remaining tablespoon olive oil. Bake on a baking tray for 20 minutes. Flip falafel balls and bake for an additional 20 minutes, until crisp and browned.
For the tahini sauce:
Combine tahini, lemon juice and water and stir to incorporate, adding more water to achieve desired consistency. Reserve.
Toss together lettuce, tomatoes and cucumbers in a bowl. Warm pitta breads for two minutes in oven. Fill each pitta with 125g salad, 4 falafel balls and 65ml tahini sauce.