Heat the neutral oil in a nonstick skillet over medium heat until shimmering but not smoking.

Place the spring roll sheet on the pan immediately. Arrange the banana slices quickly in the center of the sheet. Fold the sides inward like an envelope, working swiftly because the pastry softens rapidly. Press the edges firmly with a spatula to seal completely. Cook until the bottom is golden brown, about 1 to 2 minutes. Carefully flip and cook the other side for another minute.

Transfer to a plate, drizzle with the condensed milk, or serve it on the side. Serve warm.