Pull the rotisserie chicken apart and discard the skin. Use kitchen shears or a knife to cut the chicken up into bite-size pieces.
Dice 1 onion and then saute the onion in a large pot with butter over medium-high heat. Add a pinch of salt and cook until the onion is tender and slightly browned.
When the onions are ready add in the reduce sodium chicken broth and increase the heat to high to bring the broth to a boil.
Once the broth is boiling add in the pasta, frozen vegetables, and tomatoes. Cook for 7 minutes or until the pasta is done.
Reduce the heat to medium and stir in the chicken, parmesan cheese, lemon juice, and pepper. Cook for 1-2 minutes then remove from the heat and serve as desired.