Prepare Onions: Place the thinly sliced onions in a bowl of cold water with a pinch of salt. Let them soak for about 10 minutes. This step helps to mellow the sharpness of the onions. After soaking, drain and rinse the onions thoroughly.
Combine Ingredients: In a large mixing bowl, combine the drained onions, red, yellow, and green bell peppers, and minced jalapeño (if using).
Add Flavorings: Stir in the chopped cilantro, lime juice, and olive oil. Mix well to ensure all the ingredients are evenly coated.
Season: Season the salsa with salt and pepper to taste. Adjust the seasoning as needed, depending on your preference for acidity and heat.
Chill: For the best flavor, cover and refrigerate the salsa for at least 30 minutes before serving. This allows the flavors to meld together.
Serve: Serve the Salsa Criolla as a condiment with your favorite dishes. It pairs wonderfully with grilled vegetables, tacos, or as a refreshing topping for salads.