Place the chickpeas, sweet potato, onion, garlic, parsley, cilantro, coriander, salt, cumin, cayenne, and black pepper into the bowl of a food processor and alternate between pulsing and blending, stopping to scrape down the sides of the bowl occasionally, until all of the ingredients in the the falafel mixture are uniform in size, but still slightly grainy in texture. Transfer the mixture to a mixing bowl and fold in the cooked millet.
Roll a small amount of the falafel mixture into a walnut sized ball or a small patty with your hands. It should hold together nicely and not fall apart. (If it seems too wet, sprinkle the mixture with a small amount of the chickpea flour, no more than a tablespoon at a time, and fold it in. Once texture is correct, sprinkle the baking soda over the falafel and stir the mixture until combined.) Repeat the shaping process with the rest of the falafel mixture and place the uncooked falafel on a large plate or baking sheet until ready to cook.
To Deep-Fry (For Crispiest Falafel)
Pour the grapeseed oil into a high-sided skillet or saucepan to a depth of 3 inches or high enough to cover the falafel. Place a thermometer into the oil and heat on medium-high until the temperature reaches 360°-375°F.
While the oil is heating, place a flattened paper grocery bag onto a baking sheet and cover it with a few clean paper towels. This will help to collect the oil as it drains off of your falafel.
When the oil is ready, fry a test falafel. The oil should bubble up and sizzle all around it. The falafel itself should stay together in one piece and not break apart at all. It should take 2-3 minutes to fry to a beautiful golden brown. If your falafel is not completely submerged flip and cook the other side until it’s nice and browned all over. Remove the cooked falafel from the oil and drain on the prepared baking sheet. Sprinkle with coarse salt while the falafel is still hot, if desired. Fry the remaining falafel in batches, being careful not to over-crowd the pan and drop the temperature of the oil.
To Pan-Fry (For Crispy Falafel)
Shape your falafel into patties, not balls. Heat a large skillet over medium-high heat. Pour 2-3 tablespoons of grape seed oil in the skillet and swirl to coat. Place the falafel patties in the skillet and cook for 2-3 minutes on each side, until crispy and browned. Transfer to a paper towel-lined plate to absorb the excess oil and sprinkle with coarse salt, if desired.
To Bake (For Not-So-Crispy Falafel)
Shape your falafel into patties, not balls. Preheat the oven to 400ºF and spray a baking sheet with an oil mister filled with grapeseed oil. Place the falafel onto the baking sheet and spray the tops with additional oil; bake for about 25 minutes, flipping halfway through cooking time, or until golden brown on the outside.
To soak the chickpeas: Place the chickpeas in a large bowl and fill with water to cover them to a depth of 3 inches. Cover the bowl with plastic wrap and leave on counter for 24 hours. The chickpeas will triple in size and absorb quite a bit of the water, so check a few times during soaking to see if you need to add more. Once the beans have soaked for 24 hours, drain and rinse well.