Step 1

Cut the onion in half, then slice each half into very thin strips. Add the onion to a bowl and sprinkle with salt. Using your fingers, massage the salt into the onions to evenly distribute it. Set the onions aside to sweat for 10 minutes.

Step 2

While the onions are sweating, seed and de-vein the bell pepper and serrano chile. Slice them into thin strips.

Step 3

Place the pepper strips, lime juice and chopped cilantro into a bowl.

Step 4

Rinse the salted onions in cold water. Drain them well, and pat them dry. Add the onions to the bowl with the other ingredients. Mix to combine.

Step 5

Add the oil. Sprinkle with salt and pepper to taste. Mix to combine.

Step 6

Cover the salsa and let it marinate in the refrigerator for 10 minutes before serving.