In a food processor, pulse onion and garlic until finely chopped. Add 1 can of drained black beans, cilantro, parsley, egg, and red pepper flakes and pulse to combine.
Transfer mixture to a large bowl, add the remaining can of drained black beans and the bread crumbs. Season with salt and pepper, to taste, and mix until well combined.
Divide mixture into 4 portions and form into patties. Place on hot oiled grill over low to medium-low heat and cook about 6 minutes on each side or until heated through.