Preheat the oven 400 degrees and position two racks, one in the lower third and the other in the center.
Line a rimmed cookie sheet with easy release aluminum foil. Toss the potatoes with 1 tablespoon olive oil and arrange them cut side down on the cookie sheet. Sprinkle them with 1/2 tablespoon kosher salt. The potatoes will take 35 minutes to bake, so you'll place them in the oven, lower rack, when you start the sauce.
Arrange the mahi mahi fillets on a large rimmed plate or Pyrex dish, in a single layer, and pour the lime juice over them. Flip them to make sure that both sides get seasoned with the lime juice. Set aside for 15 minutes to marinate.
Meanwhile, to start the sauce, heat 1/4 cup olive oil in a large (4-quart pot) over medium high. Add the onion and cook, stirring regularly, until the onions start to brown, about 5 minutes. Add the garlic and cook an additional minute. Pour in the 2 cans of fire roasted diced tomatoes along with the bay leaves, oregano, parsley, half of the olives, half of the capers, and half of the jalapenos. (The remaining olives, capers and jalapenos will be use to garnish the finished dish.) Simmer briskly, stirring frequently, for about 5 minutes to evaporate some of the liquid. Reduce the heat to medium-low, stir in 1/2 cup of water and simmer for 15 minutes. Taste and season with salt, usually about 1 teaspoon.
While the sauce is simmering, saute the mahi mahi. Remove the fillets from the lime juice and blot them dry with paper towels. Sprinkle both sides of the fish with sea salt to season. Heat 1 tablespoon of olive oil in a very large (12-inch) non-stick skillet over high heat. Once the skillet is hot, place 3 of the fillets in and sear for 2 minutes per side. Remove the fillets to a wire rack set over a rimmed cookie sheet. Add the final tablespoon olive oil and finish searing the last 3 pieces of mahi, 2 minutes per side. Add these pieces to the other pieces already on the wire rack. After the potatoes have been roasting for 25 minutes, place the cookie sheet with the wire rack on the center rack of the oven to finish cooking. Remove the fish from the oven when it's just cooked through, approximately 10 minutes, along with the potatoes.
Ladle the finished sauce onto individual dinner plates, place a piece of mahi in the center, garnish with the remaining olives, capers, and jalapeno slices, then scatter the potatoes around the fish.