Kind of a PITA, but one of the keys passed down the line from my grandma is to use raw/unsteamed fresh Hong Kong style "chow mein" noodles (the characters are 生香港式炒麵). These may or may not be readily available in your area. I honestly thought she was bonkers for a while, but over the years I've seen it mentioned in different places, so she wasn't off her rocker.
I've tried using pre-steamed or dried noodles and it's not the same. Might be all in my head though.
If you can't find them, you can also buy the pre-steamed and skip the steaming steps or the dried variety and boil it according to the package instructions, then cool it with water. I think Amazon has the prepped variety, but if you can, support our "core" mom and pop shops and head into your local Asian market and spread the love. At least in the US, the communities are suffering from some seriously violence and crime...
...but this ain't a sociopolitical thread, so pardon my digression...
Now, where were we?
I'm assuming you may already know what sauce/topping you want on the noodles, so I'll focus on how to make them crispy.
Sorry if you already know any of these steps...
TL;DR
1.) Steam noodles
2.) Fry one side; flip
3.) Fry the other side.
4.) Plate
5.) Top with your desired style of stir fry.
In depth instructions:
Ingredients:
1 package raw/Unsteamed HK style chow mein noodles
2 TBS (can be US/UK or Australian tablespoons, doesn't really matter) corn oil (or any high smoke point oil)
Equipment:
Steamer
Colander/strainer
Mixing bowl of cold water
Cooking/regular wooden chopsticks
Wok
Plate
Spatula (optional)
First off, make sure all your ingredients and equipment are prepped and staged as much as possible (this includes your sauces and other ingredients you want to add). With wok usage, timing is crucial.
There's not much wiggle room - too short and stuff's undercooked, too long and the texture is gone or it's burnt to hell.
Anyhow.
Steam the noodles on high for about 10 minutes, then dip them into cold water to stop the cooking for about 20 seconds. After that drain the noodles through a colander, and fluff/separate the noodles for about 1-2 minutes with chopsticks. Then let the noodles chill out for 3-5 minutes.
Next, heat your wok on high heat for about 2 or 3 minutes. Then, add half the oil (1 tablespoon) [corn oil or any other oil with a high smoke point]. Swirl it around the pan and let the oil heat up until it's fully hot/shimmering.
Now add your noodles to the pan.
To get the noodles crispy and golden brown, we need to cook EACH side about 7-10 minutes, occasionally turning the noodles but NOT stirring or breaking up/into the layers (otherwise the much pursued crispiness will not happen). Turning helps ensure that the entire surface of the noodles gets an even crisp (what we're after) because most stoves and pans have uneven heat distribution.
After the bottom appears the right color (7-10 minutes), using your wok skills (or a spatula) flip the noodles.
After flipping, add the final 1 tablespoon of corn oil around the rim of the noodles, so that the bottom side also gets nice and crispy. Turn the noodles occasionally, and after the second side has turned crispy and golden brown, transfer the noodles onto a plate.
Then cook your meats and aromatics, take them out of the wok, after that cook your veggies, add the meat back in with the vegetables and prep your sauce. Finally put the prepped meats, veggies, and sauce mix on top of the plated noodles.
Hope this helps. Sorry if it was too long.