Heat the vegetable or olive oil in a 4 quart Dutch oven or soup pot over medium heat until the oil shimmers.
Add the leeks, carrots, garlic, mushrooms, and the firm baby bok choy stems (reserve the leaves for later) to the pot and saute until the leeks are soft (about 5 minutes).
Add the soy sauce, broth (and water if using) and sesame oil. Increase heat and bring the soup to a light boil, stirring frequently.
If using, stir in the Better Than Bouillon paste until completely dissolved.
Carefully add the frozen potstickers to the pot, and cook according to the boil instructions on the packaging (usually just a few minutes).
Reduce heat to low and stir in the reserved baby bok choy leaves and most of the green onions (reserve about a tablespoon for the soup bowl).
Serve immediately, topping bowls of soup with more green onions and a sprinkling of sesame seeds.
