Place beans in a large bowl. Cover with cool water 2-3 inches above beans. Allow to sit at room temperature at least eight hours, or overnight. Drain and rinse.
Meanwhile, combine all cucumber yogurt sauce ingredients; mix well. Refrigerate until ready to serve.
In the bowl of a food processor, combine beans, quinoa, onion, egg, parsley, cilantro, flour, salt, cumin, garlic, baking soda, pepper, and cayenne. Pulse until mixture reaches a consistency that will hold together but isn’t completely smooth.* (see note below)
Form the mixture into 10 burger patties (about 6-oz each). Refrigerate for at least 20 minutes.
Pre-heat your grill to 350° F for direct heat.
Lightly oil the grill grates or spray with avocado oil spray. Cook patties about five minutes on each side.
Serve in a lettuce wrap (or bun, if that is your thing!) topped with tomato, onion, and cucumber yogurt sauce.
* If you don’t have a large-capacity food processor, this step is best accomplished in steps. I like to start by pulsing the beans until they are small uniform pieces. Then I mix all the ingredients in a large bowl and work in batches in the food processor to get to that almost-smooth texture that holds together.