Heat a large cast iron skillet over medium-high heat. Meanwhile, vigorously beat eggs with salt using a fork until they increase a bit in volume. Stir in tomatoes, red onion, and jalapeño.
Heat oil in skillet until shimmering hot. Give eggs another quick beat, then pour into skillet, tilting to spread evenly. Cook until underside is set and golden brown (about a minute), then fold the sides in toward the centre. Flip the omelette, turn off the heat, and let stand until the centre is set - about two minutes.
Serve with pita bread or tortilla with a thin spreading of mayo and mango pickle on the side, if you like! Use the bread to pick up the egg.