Start by bringing a pot of water to a boil. There's no need to add salt.

In a skillet, heat 1 tablespoon of sesame oil over medium-high heat. Add sliced mushrooms and sauté for 5-6 minutes until tender and golden brown.

Whisk together white miso paste, seasoned rice vinegar, the remaining tablespoon of sesame oil, and gluten-free soy sauce in a small bowl until smooth.

Toss in the minced garlic to the skillet with the mushrooms and sauté for another minute.

Gently slide the soba noodles into the boiling water and cook for 4 minutes. Drain them without rinsing.

Add half of the fresh spinach to the skillet, stirring until wilted; repeat with the second half.

Pour the prepared miso sauce over the mushrooms and spinach, stirring well to combine. Let it simmer for 2-3 minutes.

Gradually add the drained soba noodles into the skillet, mixing gently with sauce, mushrooms, and spinach.

Dish the noodles into bowls and finish with a sprinkle of chopped scallions, peanuts, and sesame seeds.