Place the bacon in a large skillet and place it over medium heat. Fry the bacon, turning frequently, until crisp, about 4 to 6 minutes. Remove the bacon to a paper towel-lined plate and set aside.
Add the ground beef and onions to the drippings in the skillet. If you didn’t cook bacon or don’t have enough drippings, add a little oil to the pan. Cook the beef, breaking it up and stirring, for 4 minutes. Add the chopped peppers and garlic and continue cooking for 3 minutes longer or until the beef is no longer pink.
Add the noodles, beef broth, tomatoes, tomato sauce, Italian seasoning, 1/2 teaspoon of salt, pepper, and crushed red pepper flakes. Bring to a simmer and reduce the heat to low. Cover the pan and simmer for 15 to 20 minutes or until the noodles are tender and most of the liquid has been absorbed. Check and add extra water or broth if needed. Taste and adjust the seasonings.
Top with mozzarella cheese, cover the pan, and let it cook for a minute or two, just until the cheese is melted.