In a large bowl add the black beans and kidney beans. Mash lightly with a potato masher and then add in the corn, onion, panko, egg, garlic powder and salt and pepper.
Form into 5 large patties. Place on a plate, cover and refrigerate until ready to cook.
Heat a large skillet or grill pan over medium high heat. Add the oil and once hot, cook patties for 4 minutes on each side or until lightly browned.
Remove from the heat and top with optional toppings.
Notes
Slightly Adapted from: Cooking Light, September 2004