In a Dutch oven over medium heat, add the olive oil. Add the ground beef and cook until no longer pink (while breaking into small pieces). I like to salt and pepper the meat while it's cooking. Spoon out any excess grease.
Add in the onion, bell pepper, squash, corn, and garlic and stir. Cook until the vegetables are tender, about 5 minutes.
Pour in the tomato sauce and diced tomatoes. Add salt and pepper to taste and the sugar and bring to a simmer. Reduce the heat to medium-low and cook until slightly reduced, about 10 minutes.
While the beef mixture is simmering, cook the shells & cheese according to the package directions.
Add the mac to the beef mixture, stir to combine, and serve hot.