I made up this recipe years ago with ingredients I had around the house. Since then it's been my most requested potluck/picnic recipe. Everyone is always amazed at how simple and tasty it is. Sometimes I like to replace one of the cans of mixed beans with chickpeas. The amounts are estimates and aren't really that important, you can just make it to taste. If you want to add cucumbers wait to add them until just before serving, otherwise they'll get soggy.
In my area there is a greek restaurant (Rendezvous) that sells their house dressing bottled. This is the one I use. So just use whatever your favorite greek salad dressing happens to be. I've made this salad just with Extra Virgin Olive Oil, Balsamic Vinegar, Lemon Juice, Oregano and minced garlic for the dressing, You can also use freshly cooked dry beans in place of canned.