1 red onion, halved and thinly sliced
3 tbsp. rice vinegar
3 cucumbers, peeled, seeded and thinly sliced
salt and pepper
2 tbsp. olive oil
2 tbsp. chopped fresh dill (or 1 tbsp. dried)
Toss onion with 1 tbsp. vinegar; set aside. Place cucumbers in a colander an toss with 1/4 tsp. salt. Drain for 10 minutes. Pat dry.
Mix onion and cucumbers in a large bowl. Toss with olive oil and remaining 2 tbsp. vinegar. Add dill; season with salt and pepper. Cover and chill until ready to serve.
I found this recipe here exactly as I've written it above. The only change I made was add a little more salt.