Heat the oil in a large saucepan over medium-high heat for about 2 minutes.
Stir in the onions, carrots, celery, and ground beef. Season with kosher salt and black pepper.
Cook, stirring frequently and breaking up the meat into small chunks, until the vegetables are tender-crisp and the meat is no longer raw (it can still be pink, that's OK), about 5 minutes.
Add the garlic, oregano, rosemary, and red pepper flakes. Cook, stirring, for one more minute.
Stir in the beef broth, tomatoes, and bay leaf. Bring to a boil. Reduce the heat to medium and cook, uncovered, stirring occasionally, for 20 minutes.
Remove the bay leaf. Turn the heat off and stir in the parmesan. Divide the soup into bowls and serve.
Video
Notes
If you can't find Pomi chopped tomatoes, you can use one (14 oz) can of petite diced tomatoes (undrained) plus one (14 oz) can of tomato puree or plain tomato sauce.
You'll need to adjust the salt in this recipe according to the products you use. I use regular beef broth, but the Italian tomatoes I use are low in sodium. If you use reduced-sodium broth, consider adding more salt, unless the tomatoes you use are high in sodium. In short, taste and decide for yourself. :)
The parmesan is a bit messy - it creates a thin sticky film on the bottom of the saucepan. It's not difficult to scrub with warm soapy water, and the parmesan's thickening effect and amazing flavor are well worth it.