Heat up a large pot of water, bring to a boil, add salt, and cook pasta according to the package's instructions. Meanwhile, chop up the onion, asparagus (I trimmed off the ends and then cut into pieces), and tomatoes. Heat a skillet to medium, add the oil or butter, followed by the onion, then cook for 5 minutes or until the onion is tender.Reduce heat to medium-low, stir in the asparagus and tomatoes (put in a bit more oil if needed), cover skillet partially with a lid, and cook until the asparagus is fork tender (or your desired crispness). Season with salt and pepper to taste, and remove from heat until ready to stir into pasta. Prepare the creamy pesto sauce according to the directions in the post (it only takes a few minutes).When the pasta is ready, drain off the water, place the noodles back into the same pot, and pour in the cooked veggies + pesto sauce. Stir gently, top with extra cheese (if desired) and serve immediately.