Heat a grill or grill pan over medium-low heat. Meanwhile, in a food processor, pulse onion and garlic until finely chopped.
Add 1 can black beans, cilantro, parsley, egg, and red pepper flakes and pulse to combine.
Transfer mixture to a large mixing bowl, add the remaining can of black beans, quinoa, and the bread crumbs. Season with salt and pepper, to taste, and mix until well combined.
Divide mixture into 6 portions and form into patties.
Place on hot oiled grill over medium-low heat and cook about 6 minutes a side or until heated through.
Toast hamburger buns on a grill. Place a burger on the bottom of each bun. Top with baby spinach (or lettuce), tomato, onions, and ketchup.
Cover the burgers with the top of the bun and serve.