In a small saucepan, bring the water to a gentle boil over medium-high heat.
Stir in the rolled oats, reduce the heat to low, and simmer for 5-7 minutes until the oats are creamy and the water is absorbed.
While the oats cook, boil a separate small pot of water and cook the egg for 6.5 minutes, then immediately transfer to an ice bath to stop the cooking.
In a small ramekin, whisk the miso paste with 1 tablespoon of warm water until smooth and lump-free.
Fold the miso mixture and the fresh spinach into the cooked oats, stirring until the spinach is just wilted.
Transfer the oats to a bowl and top with the pre-cooked shredded chicken breast.
Peel the egg, slice it in half to reveal the jammy yolk, and place it on top of the bowl.
Finish by drizzling with toasted sesame oil and garnishing with sliced green onions, sea salt, and black pepper.