Preheat oven to 350 F. On baking sheet,spread black beans and bake for 15 minutes. Mash beans while on baking sheetwith the back of a fork.
While beans are baking, boil sweet potatountil soft and fork tender. Drain and mash. Set aside 1/3 cup and let cool.
Into bowl with sweet potato mash, add bakedbeans, chilies, red bell pepper, cilantro, spices, garlic, flour, green onions,lime zest, and salt (if using). Mix to combine.
Divide mixture into 4 portions and, withyour hands, form 4 patties approximately 3/4 inch thick. Place in fridge orfreezer for approximately 15 to 30 minutes (optional).
In nonstick or lightly oiled pan orbarbecue plate, on medium-high heat, cook on each side for 3 or 4 minutes. Theburgers should be warmed through and form a nice crust along the outside.
Divide torn lettuce among 4 bowls. Place aburger on top of each, then add tomato, avocado, and red onion. For additionalheat, add chopped jalapenos or your favorite hot sauce or chipotle mayo andcrumble tortilla chips (store-bought or homemade) overtop for a touch ofcrunch. Finish with a squeeze of lime.