Whisk together the olive oil, vinegar and oregano in a small bowl. Salt and pepper to taste. Set aside.
Combine the cucumbers, tomatoes, onion, parsley and feta in a medium-sized bowl. Then pour the vinaigrette over the top and toss until combined. Add more feta, parsley and S&P to taste. Refrigerate at least 15 minutes before serving.
Feel free to add in 1/4 cup sliced olives and 1/2 cup chickpeas to turn into a cucumber Greek salad.
To store: Place in an airtight container and refrigerate for up to 3 days.
To make ahead: Chop veggies and make dressing, then refrigerate. When ready to serve, mix together and chill at least 15 minutes prior to enjoying.