Crumble and layer half of the cornbread in the bottom of a large glass bowl or trifle dish. Next, add half of each in layers: lettuce, black beans, diced tomatoes, bacon, cheese, and avocados. Sprinkle 1 tablespoon of lime juice on top of avocados to prevent from browning. Repeat layers and top final salad with remaining tablespoon of lime juice. Top or serve with sour cream, if desired.