Dice your potatoes into bite size pieces. Add the potatoes to a large pot of salted water and bring to a boil. Boil potatoes until tender. Drain and add back to pot over high heat until potatoes are dry. Mix olive oil, vinegar, dijon mustard and garlic well. Pour over warm potatoes. Season with salt (it will take a lot of salt) and pepper to your liking. Mix in green onions when cooled. Serve at room temperature.