Preparation:
Wash the capers and cover with half water and half milk for at least 20 minutes to remove saltiness.

Meanwhile, warm 1/2 cup of extra virgin olive oil in a medium sized pan and cook the sliced onions stirring occasionally over medium high heat until soft, about ten minutes. Do not brown.
Once soft, add the vinegar and the sugar and stir over high heat for another 3-5 minutes until vinegar has evaporated and onions caramelized. Taste, add some sea salt and adjust flavours. Add the capers and half the mint leaves.
Let onions rest.

Pat the fish fillets dry and cook in a medium sized pan with a drop of olive oil over medium heat.

Place fish on a serving dish, top with the onions and garnish with mint leaves.

Best to let the onions and fish rest even for just an hour for the sweet and sour to amalgamate.

Serve at room temperature.