Dice the tomatoes into medium-small pieces and place them in a large bowl.
Dice the cucumber, thinly slice the pepper, and finely slice the onion. Add them to the bowl along with the chopped parsley.
Gently toss the vegetables together until evenly combined.
Drizzle with sunflower oil and red wine vinegar.
Add a small amount of salt if needed, keeping in mind that the sirene cheese is already salty.
Finely grate the sirene cheese generously over the top of the salad until most of the vegetables are covered.
Serve immediately while fresh and chilled.