Rinse dried chickpeas under tap and place in large bowl. Sprinkle baking soda (if using) and add enough water to completely submerge by at least 2 inches. Soak overnight but not longer than 24 hours. Rinse and drain before using.
In bowl of food processor fitted with metal blade, add drained chickpeas, herbs, onions, garlic, and spices. Pulse about 30 seconds at a time until the mixture is a minced fine grain. It will take several pulses to reach correct texture. Do not puree but the mixture is definitely dough-like with no individual ingredients visable. The mixture should hold its shape if you squeeze a portion in your hands. Scrape falafel mixture into a large bowl and cover tightly. Refrigerate for about 30 minutes or preferably overnight.
Just before ready to shape, heat oil in frying pan to about 350°F - 375°F on medium-high heat. Add baking powder to mixture and use a spatula to combine well.
To shape the falafels, you can use a traditional scoop tool, a tablespoon, an ice cream scooper, or even your hands, ensuring that they hold their shape. Slip the patties into the hot oil and fry for 3 to five minutes, turning halfway through. Remove when crispy and medium brown on the outside. Avoid crowding the falafels in saucepan and fry them in batches if necessary.
Place on paper-lined plate to drain. Continue until all patties are cooked.
Serve hot with pita bread and tahini sauce, tomatoes, and onions. (Makes about 24 patties.)