Add tomatoes, onion, garlic, and oil to a large saucepan over medium heat, stirring occasionally for 5 minutes.
Next, add tomato paste, harissa, oregano, broth, water, salt, and pepper to the saucepan and bring mixture to a boil. Then, cover and reduce to a simmer for 10 minutes or until tomatoes are soft.
Use an immersion blender to blend everything in the saucepan until smooth. Alternatively, you can pour everything into a blender and blend until smooth. If you use a blender, pour soup back into the saucepan afterward.
Add pasta and cook over medium-low heat for 10 minutes or until pasta is soft.
Pour soup into bowls, add a drizzle of milk (optional) and enjoy!