Heat olive oil in a large pot over medium heat. While the oil is heating, dice up the bacon, celery, onions, and garlic.
Once the oil is hot, add the diced bacon. Cook until the bacon is about 75% cooked. Then add celery and onions.
When the onions are translucent and soft, add all of the spices - salt, pepper, oregano, minced garlic, and red pepper flakes.
Cook for a few minutes, until garlic is fragrant, then add diced tomatoes and chicken broth. Bring this to a boil.
If you are going to add Italian sausage, begin cooking that now in a skillet. Once it is fully cooked, set it off to the side to drain on a towel while you finish cooking your soup.
Once the broth is boiling, add the ditalini pasta. Cook the pasta for 10 - 15 minutes, until the pasta is tender. Make sure to stir this pretty regularly throughout the cooking process to ensure that the pasta does not get stuck to the bottom of the pot. If you want to add a little more flavor, you can add the rind of a block of parmesan cheese. (I save the parmesan rinds in the freezer when we finish up a block.)
Once the pasta is tender, add the cannellini beans (and Italian sausage if you're using it.) Cook for about 5 more minutes, until the beans are nice and soft.
Remove from heat and serve with grated parmesan cheese on top.