Heat 1 tablespoon oil in a cast-iron skillet. Add sausage and cook until brown. Remove and set aside.
Heat remaining tablespoon of oil; add onion and garlic and cook until softened, about 2 minutes.
Add mushrooms in batches and cook until tender, about 3 minutes. Add fiddleheads and cook until tender but slightly crunchy, about 3 minutes more.
Add beans and wine. Simmer until liquid has reduced by half. Season with salt and pepper.