Add all ramen broth ingredients to a large dutch oven or stockpot. Bring to a boil, then reduce heat to MED/MED-LOW and simmer 15-20 minutes.
While broth is simmering, season chicken thighs with black pepper. Heat vegetable oil in a skillet over MED-HIGH heat, and cook chicken thighs, 4-5 minutes per side, until golden brown.
Whisk together remaining glazed chicken ingredients (light soy sauce, dark soy sauce, brown sugar, ginger and garlic), then pour over chicken thighs in skillet. Cook mixture down until syrupy and thick, turning chicken occasionally to glaze on both sides. This usually takes about 5 minutes, but will depend on your stove.
Remove chicken thighs to a cutting board to rest a few minutes, then slice thinly.
Once ramen broth is done simmering, place a very large mixing bowl in your sink and add a colander to that. Pour broth over the colander, straining the solids from your broth. Add pot back to the stove and carefully pour the broth from the mixing bowl back into the pot.
Add mushrooms and cook for 2-3 minutes over MED heat. Add spinach and sesame oil and cook another 3 minutes.
Add water to another pot and boil ramen noodles 1 minute less than the package directions specify. Drain, and divide among 4 bowls.
Top bowls with the hot ramen broth with mushrooms and spinach, then top with sliced chicken and green onions. Add any additional toppings you'd like and serve hot.