Ceviche is the best way to “upgrade” a fish's flavor. Undoubtedly the best recipes come from South America and the Caribbean. Here is one from Brazil:

Ingredients

500gr fileted fish
2 medium small tomatoes
½ cup lime juice
¼ cup olive oil
Hot pepper
Salt (to taste)

Cut the fish, the tomatoes and the pepper in small pieces, add the lime juice, olive oil and salt. Put all in a container and let them marinate for 15 minutes. Serve with mojitos.