Remove all but 1 teaspoon oil from Dutch oven and heat over medium-high heat. Add garlic and ginger, and sauté until fragrant, about 30 to 45 seconds. Add chicken stock, soy sauce and sugar. Remove stems from shiitake mushrooms, slice into strips and add to broth. Bring to boil, reduce heat and simmer 10 minutes. Add baby bok choy and sliced thighs to broth and simmer about 5 minutes or until bok choy is tender and chicken is cooked through.