Set your Instant Pot to the sauté function. Add the vegetable oil and allow it to heat up.
Add the sliced onion and minced garlic. Sauté for about 2-3 minutes until the onion becomes translucent.
Stir in the sliced mushrooms and bell pepper. Cook for another 3 minutes, stirring occasionally.
Add the broccoli florets, vegetable broth, soy sauce, sesame oil, grated ginger, and some salt and pepper to the pot.
Break the soba noodles in half and gently nestle them into the mixture. Do not stir, as this will help prevent them from clumping together.
Close the lid of the Instant Pot and set the valve to sealing position. Cook on high pressure for 4 minutes.
Once the cooking time is up, carefully quick release the pressure.
Open the lid, stir the noodles gently to combine with the vegetables, and adjust seasoning if necessary.
Serve hot, garnished with chopped green onions.