Set the Instant Pot to Sauté.
When the display reads “HOT”, add olive oil.
Once oil is nice and hot, add mushrooms and sauté for about 4 minutes, stirring frequently.
Add the remaining vegetables (zucchini, carrots and bell pepper) and continue to cook for couple of minutes.
Stir in basil paste and garlic.
Make sure the bottom of the pot has nothing stuck. If there is any burned bits, or browned spots, add couple tablespoons of water to deglaze. I didn’t had to, because nothing was stuck or burned, since vegetables are high in water content and I didn’t cook the veggies for too long. But I'm emphasizing it, because this is an important step to prevent “burn” notice.
Break spaghetti in half and layer in criss cross pattern over the vegetables.
Add water and pasta sauce over the noodles. Do NOT stir after this point.
Close the lid and make sure the valve is set to “sealing”.
Set the Instant Pot to Pressure Cook/Manual for 4 minutes on high. (NOTE: It took about 14 minutes for my IP to come to pressure.)
Do quick release by carefully turning the valve to venting. And carefully open the lid.
Stir everything (it may look a little watery, but noodles will absorb all the sauce in just few minutes) and serve with freshly grated parmesan cheese.