I make these for a burger restaurant in Dominical, Costa Rica. After many tries and test runs, everyone seems to love this version. We serve it Tex-Mex style with guacamole, lettuce and tomato. I'm thinking of trying to tweak it again to include more veggies, like shredded zucchini or fresh corn kernels, but haven't tried those yet. Be sure to make homemade black beans, as canned ones mash up an ugly grey color.