Step 1

Mix vinegar, soy sauce, sugar, and a pinch of red pepper flakes in a small bowl until sugar is dissolved. Set aside.

Step 2

Place zucchini in a colander set in the sink and toss with 1/2 teaspoons salt. Let stand 10 minutes, then wring zucchini dry in a clean kitchen towel. Place zucchini in a large bowl and gently mix in egg, flour, chives, and cornstarch; season with salt and pepper.

Step 3

Heat oil in a large skillet over medium heat. Working in 2 batches, drop 1/4-cupfuls zucchini mixture into skillet, flattening slightly; cook until golden and crisp, about 3 minutes per side. Transfer fritters to a paper towel–lined plate; season with salt. Serve with soy dipping sauce.

Step 4

DO AHEAD: Fritters can be made 30 minutes ahead. Keep warm in a 200° oven.