1Preheat your oven to 180°C (350°F).
Rinse and drain the black beans, then mash them in a bowl until mostly smooth.
Finely chop the onion and add it to the mashed beans.
Season the bean mixture with salt and pepper to taste.
Form the bean mixture into 4 patties.
Place the patties on a baking sheet lined with parchment paper and bake for 15-20 minutes, flipping halfway through.
While the patties are baking, slice the tomato and avocado.
Toast the whole wheat burger buns lightly.
Once the patties are done, assemble the burgers by placing a patty on the bottom half of each bun.
Top each patty with a slice of provolone cheese, a slice of tomato, a few slices of avocado, a leaf of lettuce, and a tablespoon of salsa.
Cover with the top half of the bun and serve immediately.