Saute: Heat olive oil over medium heat in a Dutch oven. Add garlic and onion and saute for 2-3 minutes or until the onions are translucent. It's ok if the bottom of the pan begins to brown a bit, that will ultimately become flavor. Add lemon juice to deglaze the pan.
Add Veggies: Turn the heat to medium low and then add the zucchini, bell pepper, peas, corn, and mushrooms and stir. Add Italian seasoning, ground mustard, salt and pepper and stir. Saute for another 2-3 minutes before adding the diced tomatoes.
Add Stock: Add the warm stock to the pot and turn heat up to high. Add pasta and stir. Bring pot to a boil and then turn down the heat to medium high so that it's boiling, but not a rolling high boil. Cover and cook for 5 minutes.
Add Cheese: After 5 minutes, remove lid and stir. Add half of the cheese and stir again. Return lid to the pot and cover to finish cooking for another 4 minutes. After 4 minutes, stir again, turn off the heat, top the pasta with the remaining cheese. Cover to let the cheese melt and the pasta to continue to cook with the remaining heat in the pot for another 2 minutes.
Serve and Enjoy!