Dice the onion into 1/2-inch pieces, mince the garlic cloves, cut the yellow squash into 1-inch thick half-moons, and have the cherry tomatoes ready. Grate the parmesan cheese and roughly chop or tear the fresh basil leaves. This prep work ensures the cooking process moves smoothly without interruption once you start.
Set your Instant Pot to sauté mode and heat the olive oil until shimmering. Add the diced onion and cook for 2-3 minutes, stirring occasionally, until it begins to soften and turn translucent. Stir in the minced garlic and cook for about 30 seconds until fragrant, being careful not to let it burn. This aromatics base creates the foundation for all the flavors in the dish.
Turn off the sauté function and add the squash and cherry tomatoes directly to the pot with the cooked onion and garlic from Step 2. Sprinkle in the dried basil, dried oregano, salt, black pepper, and red pepper flakes, then stir everything together to distribute the seasonings evenly. Pour in the chicken broth and give the pot another good stir. I like to add the spices at this point rather than later because it allows them to hydrate and bloom with the broth, creating deeper, more integrated flavors.
Close the Instant Pot lid and move the valve to the sealing position. Set the pot to high pressure for 3-5 minutes (3 minutes will give you firmer vegetables, while 5 minutes will make them softer—choose based on your preference). Once the time is complete, perform a quick pressure release by carefully moving the valve to venting position to allow the steam to escape.
Once the pressure has fully released and you can safely open the lid, stir in the lemon juice and freshly grated parmesan cheese from Step 1. The acidity of the lemon brightens the dish and cuts through the richness of the cheese. Use a slotted spoon to serve the vegetables into bowls, allowing excess liquid to drain back into the pot, then garnish each serving with the fresh basil leaves. I prefer the slotted spoon method because it gives you a more concentrated vegetable dish rather than a soup.