Peel and crush the garlic cloves. Peel and finely chop the onion. Wash and finely chop the parsley. Dissolve the baking soda in the water.
Finely chop the chickpeas in a food processor or with a blender. Add onion, garlic, parsley, cumin, coriander, salt and baking soda mixture and blend until smooth.
Heat enough oil in a large, wide saucepan. Using an ice cream scoop, form balls from the falafel mixture. Carefully place the falafels in the oil and deep fry in batches until brown on all sides. Remove and drain on paper towels.
Cut the pita bread to make a pocket. Wash the lettuce, spin dry and pluck into bite-sized pieces. Wash the tomatoes and cut into slices or wedges.
Place lettuce, then tomatoes and then falafels in the pita pockets.