In a large saucepan, combine the chicken stock and water, and bring to a gentle boil over medium heat.
Carefully add the chicken breasts to the boiling liquid and cook for 15-20 minutes until they are fully cooked. Once done, remove the chicken from the pot and let it rest for a few minutes before shredding it with forks.
In the same pot, mix in the soy sauce, sriracha, sesame oil, garlic powder, and ground ginger, stirring well to blend the flavors.
Toss in the sliced shiitake mushrooms and let them simmer for about 5 minutes until they soften.
Introduce the ramen noodles into the pot and cook them according to the package directions, typically around 3-4 minutes.
Fold in the shredded chicken and fresh baby spinach, allowing the spinach to wilt for about 1-2 minutes.
Ladle the ramen into bowls and top with soft-boiled eggs, chopped green onions, and a sprinkle of sesame seeds if desired.