Rinse the potatoes and slice them into ¼” round pieces, leaving the skin on.
Add to a medium saucepan and cover with cold water. Bring to a boil and cook until tender, checking often so as not to overcook; about 20 minutes.
Drain in a colander.
While the potatoes are cooking, chop sundried tomatoes into pieces.
Peel the cucumbers, remove the seeds, and chop them.
In a small bowl, whisk together the olive oil, garlic, salt, and pepper. Whisk again until set.
Put the potatoes, olives, cucumbers, and onion in a bowl. Pour the mixture over the potatoes and gently toss together. The potatoes should be intact.
Add the feta and kalamata olives on top, and sprinkle with oregano.