I got the recipe for agghiotta di pesce spada (or swordfish with a sauce for the glutton) from Serious Eats a few weeks ago after buying some swordfish.The sauce was so delicious that I figured it would be good with almost any fish so I tried it with humble tilapia fillets. It totally elevated the fish. You can look up the whole recipe on Serious Eats or you can just use the portion of it below which only refers to the sauce.

Tomato olive sauce for fish

1 tablespoon extra virgin olive oil
1 medium (8-ounce; 225 g) red onion, diced
1 1/2 pounds (680 g) small tomatoes, quartered, or one 28-ounce can whole peeled tomatoes with juices, tomatoes roughly chopped 
2 tablespoons (3/4 ounce, 21 g) salted capers, rinsed of excess salt 
1/2 cup (2 ounces; 57 g) pitted mild green olives, such as Castelvetrano, halved lengthwise
2 tablespoons (1 ounce; 28 g) pine nuts, toasted 
2 tablespoons (1/4 ounce; 8 g) minced flat-leaf parsley leaves and tender stems
Red wine vinegar and/or granulated sugar, to taste (optional)

Add 1 tablespoon of oil to the skillet along with the onion. Cook, stirring and scraping the bottom of the pan, until onion has softened but not browned, about 4 minutes. Add tomatoes, capers, and olives and cook, stirring, until tomatoes have broken down and their liquid has thickened, about 5 minutes. Season with salt. If desired, add 1 or 2 teaspoons red wine vinegar and a pinch or two of sugar to balance the sauce's flavor; whether or not you decide to do this will depend on the flavor of the tomatoes you're using, and how far into agrodolce ("sweet-sour") territory you want to push the sauce.

Reduce heat to medium. Stir in pine nuts and parsley, then return fish to the pan, nestling it into the sauce and cook until warmed through. Serve hot, warm, room temperature, or chilled.