Mahi mahi is a warm water fish with sweet, firm flesh. It grills beautifully and can also be pan-seared or broiled with equal success. Here a medley of colorful roasted bell peppers stars in a zesty, piquant salsa that dresses up the fish. Try it as a flavorful topping for bruschetta, too.
Make the salsa: Cut each pepper lengthwise into 4 pieces, removing the seeds and ribs. Place the peppers in a bowl and add 1 to 2 tablespoons of olive oil, tossing to coat all surfaces.
Meanwhile, heat a grill on high. When the barbecue is hot, add the pepper slices, arranging them skin-side down on the grill. Cook until the skins blister and char, 4 to 6 minutes; using tongs, turn the peppers and cook on the other side until the peppers begin to soften, 4 to 6 minutes more. Transfer the peppers to a bowl and let them sit at room temperature until they’re cool enough to handle. Peel off the skins and discard.
Cut the peppers into 1/4-inch dice and place them in a bowl. Add the scallions, parsley, capers, garlic, 1 tablespoon of olive oil, the balsamic vinegar, and pepper flakes, and stir to combine. Season the salsa with salt and pepper to taste, adding more olive oil if desired. The salsa can be kept at room temperature for several hours. If you’re not serving it immediately, you can refrigerate it, covered, for up to 3 days. For the best flavor, return the salsa to room temperature before serving.
Prepare the fish: Rub both sides of the fish fillets with some of the remaining olive oil and season with salt and pepper. Grill the mahi mahi over medium-high heat for 4 minutes, then flip the fish and continue cooking until the desired degree of doneness, or until the fish flakes when tested with a fork, 2 to 4 minutes more (depending on the thickness of the fillets).
Serve the fish topped with a generous dollop of roasted pepper salsa.