Simmer the Broth: Combine all the ginger broth ingredients in your Dutch oven. Bring to a boil over medium-high heat, then reduce to medium-low and let it simmer for 15-20 minutes.
Sear the Chicken: While the broth simmers, season the chicken thighs with black pepper. Heat the vegetable oil in a medium skillet over medium-high heat. Sear the chicken for 4-5 minutes per side until golden.
Make the Glaze: In a small bowl, whisk together the soy sauce, dark soy sauce, brown sugar, minced ginger, and minced garlic.
Glaze the Chicken: Pour the glaze mixture over the chicken in the skillet. Cook for about 5 minutes, turning the chicken frequently to coat it evenly as the sugar caramelizes and the glaze thickens. Remove from heat and let the chicken rest before slicing.
Strain the Broth: Pour the simmered broth through a colander into a large bowl. Discard the solid aromatics, then return the clear broth to the pot and keep it warm.
Add Veggies: Add the shiitake mushrooms to the warm broth and simmer for 2-3 minutes. Stir in the spinach and sesame oil, cooking for an additional 2-3 minutes until the greens are just wilted.
Cook the Noodles: In a separate pot of boiling water, cook the ramen noodles (subtract 1 minute from the package instructions for a perfect al dente texture). Drain well.
Assemble the Bowls: Divide the cooked noodles among bowls. Ladle the hot broth, mushrooms, and spinach over the noodles. Top with the sliced glazed chicken, fresh green onions, and any desired optional toppings.