In the crockpot, combine the diced onion, garlic, carrots, and celery. Stir to mix the vegetables evenly.
Add the drained beans, diced tomatoes (with juice), vegetable broth, Italian seasoning, salt, and black pepper to the crockpot. Stir until well combined.
Cover the crockpot and cook on low for about 6 hours or high for 3 hours until the vegetables are tender.
About 30 minutes before serving, add the ditalini pasta to the soup. Stir well, cover, and let it cook until the pasta is al dente.
Once the pasta is cooked, taste and adjust seasoning if needed. Serve hot, garnished with grated Parmesan cheese and fresh parsley if desired.
Feel free to add other vegetables like zucchini or bell peppers for added nutrition.
For a vegetarian option, use vegetable broth; for a meaty version, try adding diced pancetta or sausage at the beginning.
Leftover soup can be stored in the refrigerator for up to three days and may thicken; add a little water or broth when reheating.