Start by making the vinaigrette.
Add the dressing ingredients to a large bowl. Whisk to combine.
Add the onions and mozzarella pearls and stir to combine.
Start your pasta water, and when it comes to a boil, add your pasta. (see notes below)
Cook the pasta according to the package instructions. (see notes below)
Quarter the tomatoes and add them to the bowl with the dressing.
Chop the parsley and add it to the bowl.
When the pasta is done, rinse it with cold water and drain it well.
Add the pasta to the bowl with the vinaigrette, tomatoes, and parsley.
Using a big spatula, gently mix the ingredients until well combined.
Taste and adjust the salt and pepper to your liking.
Enjoy immediately or chill in the refrigerator for 30 minutes before serving.