4 sprigs oregano
2 15.5-oz. cans cannellini (white kidney) beans, rinsed
½ cup Castelvetrano olives, pitted, torn
Kosher salt
1½ lb. whole skinless whitefish fillet (such as cod, haddock, or halibut)
2 small shallots, thinly sliced into rings
1 Fresno chile, very thinly sliced into rings
2 lemons, divided
5 Tbsp. extra-virgin olive oil