Jamón-Wrapped Spanish Tortilla With Piquillo Relish

Mix peppers, olives, vinegar, and 1/3 cup oil in a small bowl; season with salt. Let relish sit at room temperature 1 hour to let flavors meld.
Meanwhile, heat potatoes and remaining 1 2/3 cups oil in a small saucepan over medium until oil begins to bubble; reduce heat to medium-low and cook, turning potatoes occasionally, until tender but not browned, 25–30 minutes. Transfer potatoes to a rimmed baking sheet with a slotted spoon; let cool slightly. Flatten with your hands and place in a large bowl. Strain oil into a measuring glass.
Heat 2 Tbsp. potato-cooking oil in a medium skillet over medium. Cook garlic, stirring occasionally, until golden, about 2 minutes. Add onion and cook, stirring occasionally, until soft and translucent, 8–10 minutes; season with salt. Transfer to bowl with potatoes. Add eggs and 1/3 cup potato-cooking oil and mix gently to combine; season with salt.
Heat 1 tsp. potato-cooking oil in a small nonstick skillet over medium. Pour in egg mixture and cook, stirring often until beginning to set and occasionally pushing away from sides to shape and compact, until golden brown and set on bottom, about 5 minutes. Press down on tortilla with spatula to flatten. Set a plate face down over skillet and swiftly invert tortilla onto plate. Slide back into skillet, browned side up, and cook until golden brown on other side, about 2 minutes. Slide tortilla onto a clean plate; let cool.
Just before serving, drape ham over tortilla and tuck ends under; spoon some relish on top.