Preheat oven to 400° F Sprinkle filets with salt and place in a shallow pan. Squeeze juice from one lime over filets. Cover with plastic wrap and marinate in refrigerator for 20 mins.
Heat olive oil in a pan over medium-low heat. Stir in onions and cook and stir until onions begin to turn translucent, 5 - 6 mins. Stir in garlic and cook until fragrant, about 30 seconds. Add capers and caper liquid, stir to combine.
Stir in tomatoes, olives and peppers. Cook and stir until pepper softens, about 4 mins. Remove from heat; stir in oregano and cilantro.
Oil or spray an oven-proof casserole dish, add 1/2 of the tomato-olive mixture, place the fillets on the mixture, squeeze the juice from half of a lime over the fish and add the remaining tomato-olive mixture. Squeeze additional lime juice over the top.
Transfer to the middle rack of the preheated oven and bake until fish is flaky and no longer translucent, 15 to 20 mins. Serve with lime wedge