Peel the white onion and slice it into very thin half-moon slices approximately 2–3 mm thick. Place the sliced onion in a bowl of cold water and allow it to soak for 10 minutes. This step reduces the onion’s harsh sulfur compounds and softens its bite while keeping its crisp texture intact. After soaking, drain the onions thoroughly in a colander and pat them dry with paper towels to remove excess moisture. Properly dried onions help the dressing cling to the vegetables rather than becoming diluted.

Wash the tomatoes and dry them carefully with a towel. Using a sharp knife, cut each tomato into thin wedges, usually 6–8 pieces depending on size. If the tomatoes contain a large amount of watery seeds, gently remove some of the interior pulp to prevent the salad from becoming overly watery. Place the tomato wedges in a large mixing bowl or directly onto a serving platter.

Wash the green and red bell peppers and remove the stems, seeds, and internal membranes. Slice the peppers into thin julienne strips about 4–5 cm long. Thin strips allow the peppers to integrate well with the tomatoes and onions, ensuring balanced flavor in every bite. Add the prepared peppers to the bowl with the tomatoes.

Add the drained onion slices to the tomatoes and bell peppers. Gently toss the vegetables together so they distribute evenly. Criolla salad can be served either mixed in a bowl or arranged attractively on a platter, depending on presentation preference.

In a small bowl combine the white wine vinegar, extra virgin olive oil, dried oregano, salt, and black pepper. Whisk the mixture vigorously for about 20 seconds until the oil and vinegar begin to emulsify slightly. The dressing should taste bright, slightly tangy, and aromatic from the oregano.

Drizzle the prepared dressing evenly over the vegetables. Toss gently using a spoon or salad tongs so the dressing coats all ingredients without breaking the tomato wedges.

Allow the salad to rest for 5–10 minutes at room temperature before serving. During this time the tomatoes release a small amount of juice that blends with the vinaigrette, creating a light natural sauce.

Sprinkle the chopped parsley evenly over the salad just before serving. Parsley adds fresh herbal brightness and enhances the visual appeal.

Serve the salad immediately at room temperature, traditionally alongside grilled meats, sausages, or roasted vegetables. It is especially popular as a refreshing side dish at Argentine asado (barbecue gatherings).