Combine the black beans, onion, garlic, chipotle peppers, adobo sauce, tamari, balsamic vinegar, cumin, salt, and pepper in a large mixing bowl. Using a potato masher, mash the mixture until it holds together but retains some texture. Add the egg and gently fold with a spatula until evenly incorporated, then fold in the panko crumbs. Shape the mixture into six patties with your hands; if the mixture feels too wet, chill it for 20 minutes or mash the beans more thoroughly. Warm a cast-iron skillet over medium heat, brush lightly with olive oil, and cook the patties for about 5 minutes per side until each is well-charred and heated through, adjusting the heat if needed. Alternatively, preheat a grill to 400°F, brush the patties with olive oil, spray the grates, and grill for about 8 minutes on the first side and 4 minutes on the second side. Serve on buns with your chosen fixings.