Prep the chickpeas the night before: Add dried chickpeas to a very large bowl. Cover the chickpeas with fresh cool water by 2 inches. Soak (uncovered) overnight to hydrate chickpeas. (They'll about double in size so make sure the bowl is large enough to accommodate!)
In the bowl of a large food processor, add the garlic, onion, and fresh parsley. Place the lid on the food processor, and pulse on and off to roughly chop the vegetables. Pause to scrape down the sides of the processor if needed. Continue pulsing until the vegetables are broken up (they should resemble a rough crumb).
Drain the soaked chickpeas and add them to the food processor. Pulse on and off until your chickpeas are finely ground (again pausing to scrape down the sides of the food processor if needed). The mixture should be very fine and crumbly at this stage.
Add in the lemon juice, all purpose flour, baking powder, salt, cumin and coriander (if using), and 4 tablespoons of water. Briefly pulse on and off to mix everything together. The mixture may look dry, but it should stick together when you squeeze it with your fingers. If it's too dry, add more water (1 tablespoon at a time) pulsing well to incorporate until the falafel mix comes together.
Divide the falafel mix and roll into golf ball sized rounds. Place your shaped falafel on a greased or parchment lined baking sheet. Set aside to preheat the oil.
Fill a high sided, large skillet with about 2 inches of neutral flavored oil like vegetable, canola, or peanut oil. Preheat the oil to 350°F. Carefully lower the balls of falafel into the heated oil. Take care not to overcrowd the skillet!
Deep fry falafel for about 3 to 4 minutes at 350°F, or until it turns a light golden brown color on all sides. Transfer the fried falafel to a paper towel lined baking sheet to drain. Repeat the frying process until all of the falafel are fried. Serve immediately as a falafel sandwich, falafel salad, plain, or however else you like!