How to Make It
Combine 3/4 cup water, 3/4 cup rice vinegar, 3 tablespoons sugar, and 1 teaspoon salt in a medium saucepan; bring to a boil. Add carrot and onion; cook 30 seconds. Remove from heat, and let stand 25 minutes. Drain.
Place pork in a medium bowl. Add 1 tablespoon fish sauce, 2 teaspoons sugar, and remaining 1/2 teaspoon salt; massage into pork. Let stand at room temperature 20 minutes.
Heat oil in a large cast-iron skillet over high heat. Add half of pork; cook 3 minutes or until lightly charred, stirring once. Remove from pan; repeat with remaining pork.
Combine 1/4 cup water, remaining 3 tablespoons rice vinegar, remaining 2 teaspoons sugar, and remaining 1 tablespoon fish sauce in a small bowl, stirring until sugar dissolves.
Arrange cucumber slices, pork, pickled onion and carrot, jalapeño, and cilantro on a platter. Drizzle evenly with dressing. Serve with cooked brown rice and chili-garlic sauce, if desired.