How to Make It
In a small bowl, whisk the sour cream with the orange juice, cilantro, lime juice, cumin, fennel and salt; cover and refrigerate.
In a medium saucepan, combine half of the chickpeas with 2 of the garlic cloves and enough water to cover by 2 inches. Bring to a boil, then simmer until well flavored, about 20 minutes. Season with salt and let cool in the liquid. Reserve 1 tablespoon of the cooking liquid.
Meanwhile, place the remaining chickpeas in the bowl of a food processor and pulse until coarsely chopped; transfer to a large bowl. Add the simmered chickpeas, remaining 2 garlic cloves, onion, bean flour, 1 teaspoon salt, baking powder, chile powder, pepper, orange zest, lemon zest, oil and reserved cooking liquid to the food processor and process until coarsely pureed. Add the falafel mixture to the chopped chickpeas and mix well. Refrigerate for at least 1 hour.
Using a 1 1/2-inch scoop or a heaping tablespoon, form the falafel mixture into balls.
In a deep pot, heat 3 inches of oil to 375º. Working in batches, fry the falafel until golden brown, 5 to 6 minutes; drain on paper towels and repeat. Serve the falafel in the warmed tortillas with tomatoes, cucumbers, avocados and onions, and pass the crema at the table.