I adapted this from a recipe in Elizabeth Andoh's Washoku. I simplified mine and didn't add the cornstarch that she calls for.
1 sliced leek
about 1/4 cup mushrooms, sliced
1/2 sweet potato, diced
1/2 butternut squash, diced
about 1/2 cup diced firm tofu
about 1 cup shredded greens (cabbage, kale, collards, etc)
Sautee everything except the greens in 1-2 tablespoons vegetable oil. Sauteeing the root veggies helps them keep their shape in the broth. Add whatever broth you want (dashi, chicken, veggie) enough to cover. I used water with a little boullion paste and a piece of kombu. Add the greens. Simmer gently until the root vegetables are tender.
You can pretty much put any kind of root vegetable in this.