Slice the onion into rings, aiming for 3-4 rings per onion.

Remove the inner parts of the onion to create clean rings. Discard uneven pieces.

Place the onion rings in a plastic bag with 2 tbsp of cornstarch and shake to coat evenly.

Finely chop the remaining onion, red chili, and any other vegetables using a food processor or knife.

In a bowl, mix the chopped vegetables, tuna, eggs, and 2 tbsp of pancake flour. Stir until well combined.

Heat a pan with cooking oil over medium heat, then reduce to low-medium heat.

Place the onion rings on the pan and fill each ring with the prepared mixture.