Thinly slice red onion into rings.

In a shallow dish, combine sliced onions with salt and sugar.

Pour white vinegar over the onions, ensuring they are submerged.

Set aside to pickle for at least 30 minutes.

Hard boil quail eggs for 5 minutes.

Drain boiled eggs and immediately soak in cold water.

Peel the eggs underwater to remove any shell fragments.

Drain and reserve the peeled quail eggs.

In a bowl, mix ground chicken with minced scallions, cilantro, salt, and pepper.

Fry a small piece of the chicken mixture to taste and adjust seasoning.

Divide the chicken mixture into 18 equal portions.

Wet your hands to prevent sticking.

Flatten a portion of chicken in your palm.

Place a peeled quail egg in the center.

Wrap the chicken around the egg, ensuring it's completely covered.

Roll the chicken-covered egg into a meatball shape.

Repeat with remaining eggs and chicken mixture.

Dip each meatball into beaten egg.

Roll the egg-coated meatball in breadcrumbs, ensuring even coverage.

Heat oil in a frying pan.

Fry the meatballs on all sides until golden brown, about 4-5 minutes.

Drain the fried meatballs on paper towels to remove excess oil.

Allow the meatballs to cool slightly.

Just before serving, slice the meatballs in half to reveal the quail egg.

Serve the sliced Scotch quail eggs with the quick-pickled onions on the side.