Preheat the oven at 175°C/347°F.
Wash the aromatic herbs with plenty of water and drain well.
Wash the canned black beans with plenty of water, drain well and place in the food processor, together with the bread crumbs and olive oil.
Pulse one or two times; don't over process, because you need texture for making the burgers.
Transfer the mixture into a large bowl.
Add the egg, parsley, onion and garlic, and mix with an wooden spoon, to combine.
Season with salt and freshly ground black pepper.
Line a baking tray with parchment paper.
Use your hands to shape little black bean balls, line on the baking tray, and press with your palms to create burger shapes.
Bake for eight minutes on one side, then flip over and bake for eight more minutes.
While the burgers are baking, prepare the avocado sauce.
Peel the avocado, remove the stone, cut roughly and place in the food processor, together with the coriander, mint leaves and lime juice. Process to obtain a creamy sauce.
Remove the burgers from the oven and set aside to cool.
Assemble the burgers in the buns, topping them with plenty of avocado sauce.