Step 1Trim the onions and cut the white parts off the green stalks. Dice the whites and thinly slice the greens.
Step 2Heat the oil in a large nonstick skillet over medium-high heat. Add the diced spring onions and sliced onion whites. Season with salt and cook, stirring often, until softened and lightly browned, 2 to 3 minutes.
Step 3Add the potatoes and stir to coat with the oil, then sprinkle with the ground chile and a generous pinch of salt. Stir again and spread in an even layer. Add ½ cup water and cover. Cook, stirring once or twice, until the potatoes are tender and browned and the water evaporates, about 10 minutes.
Step 4Meanwhile, heat the tortillas on a comal, skillet, or over the open flame of a gas burner on medium-low heat until browned in spots and pliable, about 45 seconds. Stack in a clean kitchen towel or foil and wrap.
Step 5Taste the potatoes and season with more salt if needed. Divide among the warmed tortillas and smash gently. Sprinkle with the cheese and sliced spring onion greens, then top with the salsa and jalapeño slices and squeeze lime juice on top.