re: Panda Express Chow Mein - It's a thin Chinese egg noodle. There are other sizes.

Lo Mien means "tossed noodles"; while chow mein means "fried noodles".
Panda Express fries the noodles in their "MEIN" course, so it is obviously Chow Mein.
Chow Mein is with fried noodles, while Lo Mein is commonly served separately in a bowl before adding the vegies over the tops of the noodles, (vegies served in their own dish).
Which means that both the Chow and Lo noodles are the same noodles, just when you boil the noodles for either course; you stop at just boiling the Lo, where you continue on to fry the Chow.
So if served correctly the Chinese egg noodles are cooked twice, (boiled and then fried), in chow mein. And the Chinese egg noodles are cooked once, (boiled only), in lo mein.
You can even substitute Fettucini or Linguini for Chinese egg noodles.
Chinese egg noodles are basically wheat flour noodles with egg added.
If you get the Chinese egg noodles; use the thin ones! You will definitely see that golden color.
Either course the Chinese egg noodles should be boiled as the Italians say, "Al Dente".