Add the lentils to a bowl, cover with water to soak for 1 hour, then drain.
Add the drained lentils, onion, garlic, parsley, coriander, 1 teaspoon cumin, and 1 teaspoon salt to a food processor and blend until all the lentils are broken down.
Transfer to a bowl and stir in the flour.
Form the mixture into 16-18 small patties.
Add the oil to a large frying pan and bring the heat to medium.
Cook the falafel for about 8 minutes on each side until browned. You may have to work in batches.
In a small bowl combine the tahini, lemon juice, 3 tablespoons water, remaining ½ teaspoon cumin, and remaining ½ teaspoon salt.
Slice the pita bread in half and stuff the pocket with the falafel, lettuce, grape tomatoes, pepperoncini, cucumber, and tahini sauce.