I found this recipe here: http://www.piccologrande.com/recipes/soup_Bok_Choy.htm

I modified it so that it would cook in a crock pot. It will cook great in a crock pot over Shabbos, and happily stay in that crock pot until after Shabbos is long over. I even kept it on a low setting all day, which had it happily bubbling, and had warm soup all day long . The recipe is easily doubled, if you need more soup.

2 large portabello mushrooms
6 cups water
1 mushroom vegetable bullion cube
One (1-inch) piece of fresh ginger, peeled, sliced into thin rounds, then sliced into thin strips
2 scallions, white and green parts thinly sliced or 1 medium onion, chopped
1 tablespoons vegetable oil
1 pound bok choy (about 1/2 head), sliced into 1/2-inch pieces
1/2 teaspoon kosher salt
1/8 teaspoon freshly ground black pepper
4 ounces firm bean curd, diced

I turned the crock pot on high, and chopped the vegetables right next to it. As I finished chopping them, I dropped them into the pot.

1. Turn the crock pot on high, and add the oil to the bottom. Pick the pot up and swish the oil around a little. You don't need a spatula or anything.
2. Chop up the scallions (or onions) and the ginger, and add them to the pot.
3. Cut the mushrooms in half, and then slice them in 1/8 strips. Add them to the pot.
4. Chop up the bok choy, and add to the pot.
5. Add the bean curd, water, the bullion cube, and the rest of the ingredients. Taste the broth and add salt if needed.
6. Turn the crock pot on low, and put the lid on. If this is for shabbos, do this recipe last minute. Right before candle lighting.
7. Eat the next afternoon for lunch or snack.