Peel and dice the yellow onion finely and chop the green parts of the spring onions. Dissolve the salt in the vinegar, add the chopped onions and allow them to soak for ten minutes.
Peel and seed the tomato, and dice. Seed and dice the green and red peppers.
Combine the onions with the vinegar, tomato, and peppers in a medium bowl with the olive oil and spices. Mix gently until all ingredients are well combined.
Allow the sauce to rest for at least two hours before serving.