In a medium bowl, combine the pork with half of the dark soy sauce and the sesame oil and mix to coat the meat well.
Turn on the Sauté setting on high on the Instant Pot. Add 1 tablespoon of the cooking oil. When the oil is hot, add the pork and sauté until it’s golden brown on the outside. Remove the meat from the pot.
Add the garlic to the instant pot and cook, stirring, for about 30 seconds, until it is golden.
Add the water to the instant pot and deglaze the bottom by scraping it clean with a spatula.
Add the noodles to the pot, gently pushing them down so they are under the water.
Close the Instant Pot with the lid, seal the valve, and pressure cook on high for 4 minutes.
Once the 4 minutes have passed, immediately release the natural pressure release valve, and let it rest for an additional 4 minutes.
After those 4 minutes, open the pot and stir the noodles around. Add the remaining dark soy sauce, light soy sauce, hoisin sauce, and mirin to the noodles and stir until combined well.
Then turn on the sauté setting on high and add the sliced red bell pepper, bok choy, carrots, and onions, and return the pork to the pot. Cook, stirring often, for for 5 to 8 minutes, depending on how you like your vegetables. Cook for the shorter amount of time for crisp-tender vegetables and longer for softer vegetables. Season with salt and pepper to taste.
Serve hot, garnished with sesame seeds if desired.