Preheat oven to 425 degrees F.
In a large bowl, toss potatoes with olive oil, 2 teaspoons salt, and about ½ teaspoon black pepper. Transfer to 2 large sheet pans and arrange potatoes in an even layer, without overcrowding the pan. Roast for about 30 minutes, flipping once halfway through, until tender and golden brown.
Make the dressing: in a bowl, combine mayonnaise, vinegar, dijon mustard, and salt and pepper to taste.
In a large serving bowl, add the roasted baby potatoes, blue cheese, cooked bacon, parsley, and green onions. Toss with the dressing until nicely and evenly combined. Adjust seasonings if needed or to taste. Serve and enjoy!