Lo Mein - something missing

Made a huge pile of lo mein for dinner last night. It was really good, but was missing something that I just can't put my finger on. There's some taste that the lo mein from the restaurant has that I wasn't able to replicate last night. Some...umami.

Here is a rough lineup of my ingredients, in no particular order:
peanut oil
napa cabbage
carrots
garlic
ginger
noodles
light soy
dark soy
oyster sauce
chicken broth
sugar
salt
mushrooms
char siu
shrimp
cornstarch
sesame oil

What is the missing taste? It's definitely a sauce component, not a veggie or meat. The shrimp and char siu were just perfect. Is it MSG?

What is it that makes that wonderful taste?