Combine eggs, lime juice / vinegar, fish sauce, water, and rice flour / cornstarch in a medium bowl. Beat with a fork until frothy. If the flour forms a few lumps, break up as many as possible with your fingers.

Heat the vegetable oil in a small pot or round-bottom wok set over medium-high heat until lightly smoking. Hold the egg bowl about 1 ft. above the pan and pour the egg mixture into the oil in one go.

The egg mixture will immediately puff up. Do not disturb it. After 20 sec., flip the omelet. There's no need to keep it nice and round; we want asymmetrical edges. Let the other side cook for another 20 sec. Remove the omelet from the pan and serve over steamed jasmine rice immediately.