Heat the olive oil in a large pot over medium heat. Add the onion and cook until softened, about 5 minutes. Add the garlic and cook for another minute.
Add the diced tomatoes and cook for 5 minutes. Pour in the chicken broth and bring to a boil.
Add the ditalini pasta and cook according to package instructions until al dente. Stir in the cannellini beans, oregano, salt, and pepper. Simmer for another 10 minutes.