In a blender or food processor, combine the diced tomatoes and RoTel diced tomatoes, pulse about 4 times. You don't want the tomatoes completely smooth, a little chunky is great.
In a medium dutch oven or stock pot, bring the beef broth to a low boil. Add the pureed tomatoes and boil again.
Add the tortellini, basil, green beans and red pepper flakes or cayenne pepper. Simmer until tortellini is ready, about 10 minutes.
Serve with Parmesan cheese grated on top.
I recommend eating this soup the same day it's prepared. Leftovers taste delicious but the tortellini tends to get big and overly soft the next day.
Optional variations: Tortellini can be substituted for any favorite pasta, ravioli is nice. Beans can be substituted for fresh or frozen corn.
Cook's note: I add 1 1/2 cups tortellini because I like the soup to have more broth. You can add more tortellini as you like. And if you add more tortellini, you can also increase the amount of broth to accommodate the increase in pasta. I would taste before serving to test if you need more basil as well. Also, I like the dried version of tortellini, which absorbs more of the liquid. If you use fresh tortellini, add it more towards the end of simmering, whatever the packaged directions dictate.
Stephen's recommendation for beef broth: Stephen swears by using a beef base rather than store bought broth. Minor's brand is excellent with no artificial ingredients.