Chop chipotle peppers and put in a bowl. Mix in maple syrup, vegetable broth, and tamari.
Rinse beans and add to sauce. Set aside.
Heat olive oil in pan and add chopped onion. Cook until translucent.
Add bean mixture and cook until liquid is dissolved. Add desired amount of salt and pepper. At this point I mashed the beans slightly because I wanted them to soak up more sauce, but that's up to you.
On lettuce leaves, pile on maple chipotle black beans, sliced avocado, and mango salsa.
Notes
The black bean mixture will last 5 days in an airtight container in the fridge.