Bring a large pot of salted water to a boil.

Blanch green beans for 2-3 minutes until tender-crisp.

Transfer green beans to ice water, then drain and halve.

Add potatoes to a pot, cover with salted water, and boil for 4-6 minutes until slightly tender.

Drain potatoes and let cool, then halve.

Whisk vinegar, lemon juice, mustard, honey, salt, and pepper in a large bowl.

Slowly whisk in olive oil until emulsified.

Preheat grill to medium heat.

Toss potatoes with olive oil, salt, and pepper.

Grill potatoes for 4-6 minutes, turning occasionally, until browned.

Remove potatoes from grill and toss with some of the vinaigrette.

Combine potatoes, green beans, feta, olives, and oregano in a bowl.

Add more vinaigrette and toss to combine; season with salt and pepper to taste.

Sprinkle with parsley leaves.

Serve at room temperature or chilled.