1/2 medium red onion, diced
2 cups diced tomatoes
1/4 cup chopped fresh cilantro
1 tablespoon minced jalapeño (optional)
Place 1 cup cold water and 2 ice cubes in a medium bowl.
Add onion; stir, then discard ice; drain well. Transfer to a medium bowl.
Add tomatoes, cilantro, and jalapeño, if desired. Season with salt.