Cut the onion into thin rings, leave it in boiling water for 10 minutes to remove the bitterness, then drain the water, add the onion to the cucumbers and radishes.
Remove the core from the apple and cut it into slices.
Cut the pepper into rings, put the apple and pepper in a salad bowl with the rest of the ingredients.
Finely chop the green onion, parsley and lettuce leaves into a salad bowl and add salt.