For the falafel: add the chickpeas, onion, parsley, cilantro, dill, cumin, garlic, salt, baking powder, and half of the oil into a blender or food processor and blend for 40 seconds at a time until all is well combined. Fold in the flour. Refrigerate for 20 minutes.
For the tahini sauce: Whisk all the ingredients together. Whisk in water 1 tablespoon at a time until you reach a creamy consistency. Season with salt and pepper to taste.
In the meantime, heat the remaining oil for the falafel over medium heat in a saute pan. Form mixture into equal patties about 1/2 inch thick. Fry patties in the hot oil until browned, 3 to 4 minutes per side.
In a nonstick pan on medium heat, warm the pita for 1 - 2 minutes per side.
Place the lettuce, tomatoes, falafel, olives, feta, and onion on the pita. Drizzle the sauce over top. Fold in half and serve with chips and pickle.