Add the broth to the pot and raise the heat to medium-high. Once the broth is very hot, but not boiling, place the miso in a small bowl, whisk in about 1 cup of the hot broth to make a slurry, then add that mixture back to the pot. Turn off the heat, but leave the pot on the burner, and add the green parts of the green onions, shredded turnip greens, and tofu. Let it stand for a moment to heat everything through and wilt the greens, then serve immediately.