Heat oil in large sauce pan over medium-high heat. Add onion, celery, carrot, garlic, tomato paste and thyme. Cook, stirring until vegetables are just starting to brown, 3-5 minutes. Add broth, water, tomatoes (with juice) and potatoes; bring to a simmer over high heat. Reduce heat to maintain a simmer and cook until potatoes are tender, 12-15 minutes. Add cod, cook gently, stirring occasionally, until just cooked through, 4-5 minutes more. Season with salt and pepper.
**If you wish, you could also add old bay seasoning, hot sauce, sausage or chicken.