In a pot, sauté the mushrooms for 5 minutes on medium-high heat. After, reserve one tablespoon for topping and fill the pot with the water. Bring to a boil and let it simmer for 10 minutes on medium heat.
Reduce the heat to medium-low, add oatmeal and cook for 5 minutes (until it slightly thickens).
Add the soy sauce, rice vinegar, sugar and grate in the garlic and ginger. Stir and let it cook until it reaches your desired consistency (5-8 minutes). Turn off the heat and stir in the miso paste.
Add the oatmeal to a bowl, add the reserved mushrooms, pour over the sesame oil and garnish with the scallion.
