Start by heating the oil in your Instant Pot. You will know it is ready when it shimmers a bit, giving off a lovely warmth. This step is essential for softening the onion and jalapeño. Do not skip it, or your veggies might just steam instead of sautéing!
Add in the diced onion and jalapeño, stirring them until fragrant and the onion appears translucent. This should only take a few minutes. Keep an eye on them to prevent burning—bitter flavors can ruin your dish!
Toss in the black beans, mushrooms, red peppers, corn if using, pasta shells, taco seasoning, salsa, and vegetable broth. Mix it all up until evenly distributed. If you do not mix well, some areas might be overloaded with flavor while others remain bland.
Seal your Instant Pot and set it to pressure cook on high, letting it do its thing. You will hear it hiss, and soon the aroma will waft through the kitchen. Ensure you do not release pressure too early—wait for the cook cycle to finish first!
Once the cooking time is up, do a quick release on the pressure. Be cautious of the escaping steam, as it can be hot. This step helps keep the pasta from getting mushy, which is a common issue if you let it sit too long.
Open the lid carefully and stir in the grated pepper jack cheese. Watch it melt into the pasta. For an extra layer, top with chopped cilantro and diced avocado. This is when it becomes colorful and appetizing, so plate it up before it cools down!