Bring a large pot of salted water to a boil. Cook the pasta until al dente according to package instructions. Drain and rinse under cold water until completely cooled.
Soak the sliced red onions in cold salted water for 10 minutes to mellow their sharpness. Drain well.
In a small jar with a lid, combine lemon juice, lemon zest, garlic, parsley, olive oil, oregano, salt, and pepper. Shake vigorously until well blended. Adjust seasoning as needed.
In a large mixing bowl, combine cooled pasta, drained onions, red bell pepper, cherry tomatoes, olives, feta, cucumber, and parsley.
Pour 1/4 cup of the lemon olive oil dressing over the salad and toss gently. Add more dressing gradually if desired.
Season with additional salt and pepper to taste. Chill for at least 30 minutes before serving for best flavor.
This Greek Pasta Salad tastes even better after the flavors meld together.