Make the pickled onion: Combine the red onion, lime juice, olive oil, oregano and 1/2 teaspoon salt in a small bowl. Let stand 30 minutes or up to 1 day; drain.
Meanwhile, make the sauce: Fill a medium pot with water and add the tomatoes, onion and garlic. Bring to a boil and turn off the heat; let cool. Drain the ingredients, then transfer to a blender and puree until smooth; season with salt. Heat the vegetable oil in a medium saucepan; add the tomato mixture and cook until slightly reduced, about 10 minutes. Set aside.
Prepare the jalapenos: Heat 1/2 inch vegetable oil in a large saute pan over medium-high heat until very hot. Fry the jalapenos until blistered, 3 to 4 minutes per side. Transfer to a paper towel-lined plate to drain, then place in a bowl and tightly cover with plastic wrap. Let steam about 15 minutes, then peel off the blistered skins using a paring knife or rub with a kitchen towel. Using a sharp small knife, cut a T in each jalapeno, starting at the top of the pepper and running almost to the bottom. Using a very small spoon or the tip of the knife, carefully remove the seeds and veins. Set the peppers aside.
Make the filling: Heat 1 tablespoon vegetable oil in a medium skillet. Add the potato and cook, stirring, until golden and crisp, about 10 minutes. Transfer to a plate using a slotted spoon. Add the carrot, onion and garlic to the skillet; cook, stirring, until fragrant, 5 minutes. Add the beef and cook, breaking up the meat, until it starts browning, about 5 minutes. Add the raisins and potato. Cook, stirring, until the meat is cooked through, about 10 more minutes. Season with salt and pepper.
Reheat the sauce, adding up to 1/2 cup water if it is too thick. Divide the beef mixture among the jalapenos. Top with the tomato sauce and pickled red onion.
Photograph by Dave Lauridsen
Recipe courtesy of Marcela Valladolid for Food Network Magazine