In a two-liter cast iron oven over medium-high heat, cook the onion in the oil until softened, stirring a few times. Add the water and soup mix and stir to combine. Bring to a boil and simmer for 5 minutes.
Add the turnips greens and simmer 10 minutes.
Add the beans and sausage and simmer until the greens are tender, about another 15 minutes. If you want it more “soupy,” add hot water.