Load the slow cooker. Add all ingredients from the mushrooms through the ground ginger into the slow cooker. Give everything a good stir to combine.
Cook. Cover and cook on high for 4 hours or low for 8 hours.
Add bok choy and noodles. In the final 3–5 minutes of cook time, add the bok choy and noodles directly to the slow cooker. Cook on low until the noodles are just cooked through.
Taste and adjust. Stir everything together and taste the broth. Add more soy sauce for saltiness, a splash more rice vinegar for brightness, or extra ginger for warmth.
Serve immediately. Ladle into deep bowls and top with sliced green onion, sesame seeds, and chili oil.
The Broth The Most Important Decision You'll Make
Let's talk about broth for a moment, because this is where a lot of vegan noodle soups fall flat and this one doesn't.
Use Vegan Chicken-Style Broth If You Can Find It
Standard vegetable broth is fine, but it often tastes thin and slightly sweet in a way that doesn't hold up to four hours of slow cooking. Vegan chicken-style broth has significantly more depth and a savory, rounded flavor that makes the finished soup taste genuinely rich and complex. If you can find it at your local store or online, use it. The difference is noticeable.
Working With Regular Vegetable Broth
If vegan chicken broth isn't available, regular vegetable broth works you just need to compensate for its milder flavor:
Add an extra tablespoon of soy sauce to deepen the saltiness and umami.
Stir in a tablespoon of white or yellow miso paste near the end of cooking for extra depth.
Use 6 cups of broth and 2 cups of water if you're sensitive to salt this balances the sodium without sacrificing too much flavor.
FYI, the mushrooms do a lot of the heavy lifting here regardless of which broth you use. Four hours of slow cooking with shiitake and hon-shimeji mushrooms will enrich almost any liquid.
The Noodle Situation This Matters More Than You Think
Ever added noodles to a slow cooker too early and ended up with a bowl of paste? Yeah, we're not doing that. Noodles go in during the last 3–5 minutes only, and even then you need to think about whether you're eating all four servings at once or saving some for later.
If You're Eating Everything Right Now
Add the noodles directly to the slow cooker in the last few minutes and let them cook in the broth. Chuka soba noodles (Japanese soba-style noodles) work brilliantly here they cook quickly, have a satisfying chew, and absorb the broth beautifully without falling apart.
If You're Meal Prepping or Saving Leftovers
Cook the noodles separately in a pot of boiling water and add them directly to individual bowls at serving time. This is the move for meal prep. Noodles left sitting in hot broth even in the fridge continue absorbing liquid and turn soft and gummy. Keeping them separate means your leftover portions taste just as good on day three as they did on day one.
Which Noodles Work Best
Chuka soba - the top recommendation; quick-cooking and ideal texture
Rice noodles - great gluten-free option, cook even faster
Udon - thicker, chewier, and holds up well to the bold broth
Instant ramen noodles - grab a pack, ditch the seasoning packet, and use just the noodles. Works perfectly and nobody needs to know.
Soba noodles - hearty and slightly nutty; rinse well after cooking to prevent sticking
