Cut the yellow bell pepper and zucchini into 1cm cubes. Mince the red onion and soak it in water, then drain. Quarter the cherry tomatoes.

In a bowl, mix the seasonings (white wine vinegar, sugar, salt, pepper, and olive oil). Add the prepared vegetables and mix well. Cover tightly with plastic wrap and refrigerate for 30 minutes to let the flavors meld.

Pat the horse mackerel dry and cut it into bite-sized pieces.