Rinse the sorghum under cold water. Place it in a large pot with 4 cups of the vegetable broth. Bring to a boil, then reduce to a simmer and cook for 45 minutes until the grains are tender but still chewy.

While the sorghum cooks, heat the olive oil in a skillet over medium heat. Add the mushrooms and cook until they release their liquid and turn golden, about 6 minutes. Set aside.

In a blender, combine the tomatillos, half the onion, jalapenos, garlic, and most of the cilantro with the remaining 2 cups of broth. Blend until smooth.

Pour the green sauce into the pot with the cooked sorghum. Add the salt and stir in the sautéed mushrooms. Simmer together for 10 minutes so the flavors meld.

Chop the remaining onion and cilantro. Ladle the soup into bowls and top with the fresh onion, cilantro, lime wedges, radishes, and avocado.