Heat 2 tablespoons of the oil in a saucepan, add the onion and cook for 5 minutes until softened. Add the garlic and cook for a further 30 seconds. Pour in the wine and simmer for 1–2 minutes until reduced by half.
Add the tomatoes, season and bring to the boil, then reduce the heat, add the capers, olives, jalapeño slices and oregano and simmer for 20 minutes, topping up with water if necessary.
Meanwhile, heat the remaining oil in a large nonstick frying pan, add the snapper fillets, skin-side down, and cook for 7 minutes until golden and crisp. Turn the fish over and cook for a further 5 minutes, or until the fish is just cooked through. Spoon over the sauce and serve with rice.