In a large pan or skillet, saute onions until golden, then add the sliced mushrooms and cook for 5 minutes. Add only a 1/2 cup of the cooking broth and continue cooking onions and mushrooms until that liquid almost disappears.
In a small bowl whisk the miso paste with 2 tbsp of the broth. Pour into skillet and cook. Season with sea salt and pepper. Add the remaining broth and cooked chicken, turkey or tofu. Cook for 30 minutes more over a low heat.