In a large pot or skillet, cook the ground beef and diced onion over medium heat until the beef is no longer pink. Drain excess fat.
Stir in the beef broth, tomato sauce, diced tomatoes with chilies, and taco seasoning. Mix well.
Add the uncooked pasta shells. Bring to a boil, then reduce heat to low. Cover and simmer for about 12-15 minutes, stirring occasionally, until pasta is tender.
Once the pasta is cooked, remove from heat and stir in the shredded cheddar cheese.
Serve immediately, topped with your favorite toppings like sour cream, green onions, or jalapeños.