Heat oil and butter in large Dutch oven over medium heat
Add onions. Saute, stirring occasionally until soft and golden, but not brown, 6-8 minutes
Stir in carrots and potato (if using). Saute for 5 minutes.
Stir in celery and green beans. Saute for 5 minutes.
Stir in zucchini. Saute for 3 minutes.
Stir in garlic. Cook for 1 minute.
Add broth, water and liquid from tomatoes to pan. Add chopped tomatoes to pan.
Stir in salt, basil, rosemary, pepper, bay leaf, and diced potatoes (if using).
Heat to boiling. Reduce heat to low.
Simmer, covered, stirring occasionally, for 1½ hours.
Add drained and rinsed beans. Cook uncovered over medium-low heat, stirring occasionally, until soup is thick, 30-40 minutes.
Add pre-cooked pasta or rice (if using).
Remove bay leaf.
Serve with grated Parmesan cheese sprinkled on top. Crusty bread is wonderful as an accompaniment.