Kachumbari (Kenyan Tomato and Onion Salad)

Name: Kachumbari (Kenyan Tomato and Onion Salad)
Prep time: 10 min
Total time: 50 min
Cuisine: Kenyan
Ingredients: 1 small red onion (finely chopped); 2 teaspoons salt; 4 tomatoes (diced); 1/2 cucumber (diced); 1 avocado (pit removed, peeled, and diced); 1-2 small red chile peppers (stem removed and finely diced); 1/4 cup freshly chopped cilantro; Juice from 1 lime; 1 tablespoon olive oil (optional)