Drain the water from the chickpeas and rinse 2-3 times. Cook chickpeas with 2.5 cups water and salt. I cook it for 8-10 whistles on, high flame. Switch off the gas and let the pressure drop completely, around 15 mins.
Open the cooker and separate the Kadala and stock (cooking water). You can use the stock for some veg soup or veg pasta.
Add the chickpeas, onion, garlic, parsley, coriander leaves, salt, chilli powder, pepper powder, cumin and baking powder to the bowl of the food processor and pulse until they are roughly blended but not pureed.
Add just enough flour so that when you pulse the processor, the mixture begins to form a small ball and is not sticky. (Note: Start by adding ¼ cup of flour, and then the remaining ¼ cup. You can add more if the mixture is still too wet.)
Transfer the falafel mixture to a bowl, add more flour if it's still too wet. Cover it with plastic wrap and refrigerate it for 1 hour. Once the falafel mixture has chilled, use a small ice cream scoop or spoons to form the mixture into balls (roughly 3 Tablespoons per ball). (Note: You can also add additional flour at this point, if the mixture is too wet to scoop.)
Set a large sauté pan over medium heat and add a liberal amount of oil so that the pan is well-coated. Let the pan pre-heat for 3 minutes then add the falafel one by one, browning them on the first side for 3 minutes, then flipping them once and browning the second side until the mixture is cooked throughout.
Transfer the falafel to a paper towel-lined cooling wrack. Repeat this process until you have cooked all of the falafel.
Prepare the tahini sauce by whisking together the yogurt, tahini and lemon juice. Season it with salt and pepper, cover it and place it in the fridge.
Place three or four falafel inside a halved, warmed pita and drizzle with the prepared tahini sauce.