In a 4-quart saucepan, heat the oil over medium-high heat.
2 tablespoons olive oil
When the oil is hot, add the onion, celery, carrots, and potatoes. Sauté for about 5 minutes.
1 cup sweet onion, 1 cup celery, 1 cup carrots, 8 small red potatoes
Once the vegetables begin to soften, add the tomatoes, water, Old Bay seasoning, and salt.
28 ounces diced tomatoes, 3½ cups water, ½ teaspoon Old Bay seasoning, 2 teaspoons sea salt
Use kitchen twine to tie together the sprigs of oregano and thyme plus the bay leaf. Add the herb bundle to the saucepan.
1 sprig fresh oregano, 2 sprigs fresh thyme, 1 bay leaf
Bring the mixture to a boil, then reduce the heat to medium-low and simmer for about 15 minutes or until the potatoes are tender.
Add the mahi-mahi and simmer until the fish is opaque and just cooked through, about 10 minutes.
1 pound mahi-mahi or other firm white fish
Add freshly ground pepper and serve immediately.
1½ teaspoons freshly ground black pepper